Although there have been recent advances in the development of photoprotective clothing and broad-spectrum sunscreens, few peer-reviewed publications have focused on photoprotection recommendations for travelers.
Although there have been recent advances in the development of photoprotective clothing and broad-spectrum sunscreens, few peer-reviewed publications have focused on photoprotection recommendations for travelers.
In order to describe the adverse health effects of excessive ultraviolet (UV) radiation exposures; review recent studies of public perceptions regarding photoprotection and sun exposure behaviors; identify special populations at increased risks of drug-induced photosensitivity reactions and UV-induced skin cancers; and recommend several effective photoprotection strategies for travelers, Internet search engines were queried with the key words as search terms to examine the latest references on photoprotection and the epidemiology of UV-associated skin cancers.
Observational studies have demonstrated that the public knows little about proper sunscreen protection, selection, and use, and often abuses sunscreens for intentional UV overexposures. Cohort studies have identified special populations at increased risks of UV-associated skin cancers without the proper use of sunscreens and photoprotective clothing including children, fair-skinned persons, patients taking photosensitizing drugs, and organ transplant recipients (OTRs). Clinical investigations support the regular use of broad-spectrum sunscreens to prevent the development of premalignant actinic keratoses (AK) in all sun-exposed subjects, especially OTRs; to prevent the development of squamous cell carcinomas from new AK in sun-exposed subjects, especially OTRs; to possibly prevent the development of cutaneous malignant melanomas in children and adults; and to possibly prevent the development of basal cell carcinomas in OTRs.
Recommended photoprotection strategies for travelers should include avoiding intense sunlight, wearing photoprotective clothing, wearing sunglasses, and selecting the right sunscreen for their skin type. Travel medicine practitioners should counsel travelers about photoprotection and encourage travelers to take advantage of recent advances in the development of more effective broad-spectrum sunscreens and photoprotective clothing for themselves and their children.
Sunbathing, swimming, skiing, and many other outdoor pursuits remain popular activities among travelers despite well-documented associations between excessive ultraviolet (UV) radiation and skin cancer. Although there have been recent advances in broad-spectrum sunscreens and photoprotective clothing, few peer-reviewed publications have focused on preventive strategies for excessive solar radiation exposures during travel to temperate, tropical, and high altitude regions with high UV indices. In response, the objectives of this review were (1) to describe the adverse health effects of excessive UV radiation exposures, (2) to review recent cohort studies of public perceptions regarding sun exposure and protective behaviors, (3) to identify special populations at increased risks of UV photosensitivity, and (4) to recommend simple and effective photoprotection strategies for travelers.
Internet search engines were queried with the key words as search terms to examine the latest references on photoprotection and the epidemiology of UV-associated skin cancers and other adverse effects of UV-radiation exposures. This search yielded only three references on photoprotection for travelers including a British comparison of photoprotection recommendations from five travel guides for travelers to Spain, a German article on sun and insect bite protection while outdoors, and a French article on sunglasses and sunscreens during travel to tropical areas.[1-3]
Solar UV radiation is classified by wavelength into UVA1 (340–400 nm), UVA2 (320–340 nm), UVB (290–320 nm), and UVC (100–290 nm). The stratospheric ozone layer effectively absorbs most UVB radiation and all UVC radiation; but some UVB and all UVA2 wavelengths still reach the earth's surface. UVB is mostly absorbed by the epidermis and is primarily responsible for erythema and sunburn. UVB radiation damages DNA at neighboring pyrimidine sites and can cause local mutations in p53 tumor suppressor genes with resulting squamous cell carcinomas (SCCs).[4, 5]
The skin is continuously exposed to UV radiation outdoors, receives the largest doses of radiation, and suffers the most significant adverse effects, including photoaging, sun allergy, premalignant skin lesions [actinic keratoses (AK)], and skin cancers, of which the most common types are non-melanoma skin cancers [basal cell carcinoma (BCC) and SCC] and cutaneous malignant melanoma (CMM).[6-16] Skin cancers exhibit different sun-exposure-related risk factors with early, intermittent overexposures and blistering sunburns associated with BCC and CMM, and chronic and cumulative overexposures associated with SCC.[7, 14, 17-19]
The non-melanoma skin cancers (NMSCs) comprise 95% of all skin cancers and are the most commonly occurring malignancies among fair-skinned populations worldwide.[10-13] The annual world incidence of NMSCs is estimated to be 2 to 3 million cases each year.[10-13] An upward trend in NMSCs has now been observed in Australia, Europe, and the United States (US) with an average annual increase between 3% and 8%.[10-13]
The BCC, the most common malignancy in Caucasians, now accounts for 80% to 85% of all NMSCs and 30% of all cancer diagnoses.[10-13, 17] The annual worldwide incidence rate of BCC is anticipated to increase in annual prevalence as the world population ages. BCCs usually occur as nonhealing ulcers or papulonodules on sun-exposed areas, especially on the head and neck that rarely metastasize.
The SCCs begin in the uppermost layer of the skin, account for approximately 15% of all skin cancers, and have a 10-fold greater risk for metastasis and death than BCCs.[10-13] SCCs usually occur on sun-exposed areas of the head, face, neck, and hands, and may be heralded by AK.[9-12, 19]
Cutaneous malignant melanoma (CMM) accounts for approximately 5% of skin cancers worldwide and has the highest case fatality rates. CMM is now the most commonly increasing malignant disease with an estimated annual incidence rate of 3% to 7%. The World Health Organization has estimated that 132,000 new cases of melanoma will occur each year worldwide. Melanomas are more common in fair-skinned people with light-colored eyes and blond or red hair. Besides skin type and family history, the greatest risk factors for melanomas include three or more blistering sunburns before age 18 years, congenital nevi (moles), large numbers of moles, and long-term phototherapy for eczema or psoriasis with psoralens and UVA (PUVA).[6, 7, 10, 11]
Melanomas arise from melanocytes, are usually darkly pigmented, and can occur anywhere, but occur more commonly on the trunk in men and on the legs in women.[10, 11] The characteristic physical features of melanomas, often described as the ABCDs of melanomas include: (1) asymmetric shape, (2) border irregularity, (3) combination of colors, and (4) diameters larger than a pencil eraser (6 mm). Although an association between UVB overexposures and SCCs has been well established, the exact UV wavelengths associated with BCCs and CMMs are not clearly defined.
Ezzedine and colleagues have studied sun exposure behaviors in large subcohorts of survey-responding travelers, nontravelers, and expatriates nested in a larger cohort of 12,741 French adult volunteers enrolled in the SU.VI.MAX cohort and observed the following results. (1) Women travelers reported more frequent sun exposures over the past year, sunbathed in high UV-index areas daily for more than 2 hours, and experienced more intensive sun exposures than nontravelers. (2) Although the usage of sun protection products was similar in all travelers and nontravelers, women used sunscreens with higher sun protection factors (SPFs) more often and more regularly than men.
In a similarly designed study, the same investigators sent sun exposure and sun protection behavior surveys twice to all subjects in the SU.VI.MAX cohort, with 1,694 respondents reporting travel to a tropical or high UV-index country during their lifetimes for more than three consecutive months (expatriates). The investigators described the following results. (1) Female expatriates reported more frequent deliberate sun exposures, more sunbathing between 11 am and 4 pm, less gradual sun exposure, more intensive sun exposures, more exposures during nautical sports, and more nude exposures than female nonexpatriates. (2) Male expatriates reported more frequent intensive sun exposures and more skin exposures during nautical and mountain sports than male nonexpatriates. Ezzedine and colleagues have registered a large cohort of French adults to observe for sun exposure and protection behaviors in tropical and high UV-index countries for short and prolonged stays, and their results have repeatedly demonstrated that travelers would benefit from more pre-travel advice regarding sun exposures and sun protective behaviors.[20, 21]
Observational studies have demonstrated that the public often misuses sunscreens for intentional UV overexposures and knows little about proper sunscreen protection, selection, and use. In 2001, Wright and colleagues evaluated attitudes toward sunscreen effectiveness and found that 47% of study subjects reported staying out longer in the sun after applying sunscreen. Later, Autier defined this behavior as sunscreen abuse or the misuse of sunscreens by sun-sensitive subjects engaging in intentional sun exposure to increase their duration of exposure without decreasing sunburn occurrence. In 2008, Ezzedine and colleagues reported the results of a cross-sectional study on artificial and natural tanning behaviors in a French national cohort of 7,200 adults. The investigators determined that indoor tanners were also regular sunbathers unconcerned about the risks of combined indoor and outdoor UV exposures. In a 2009 survey assessment of sunscreen knowledge, Wang observed that only 48.2% of survey respondents knew that “SPF” was the acronym for “sun protection factor.” The confusing measurement systems for UV protection afforded by sunscreens and photoprotective clothing are compared in Table 1.[18, 26, 27]
|Measurement system||Sun protection factor (SPF)||UVA-protection factor (UVA-PF)||Ultraviolet protection factor (UPF)|
|Definition||The minimal erythema dose (MED) of UVB radiation causing erythema after applying 2 mg/cm2 of sunscreen to skin divided by the dose producing 1 MED on unprotected skin.||The dose of UVA causing observable pigment darkening (minimal pigment dose [MPD]) after applying 2 mg/cm2 of sunscreen to skin divided by the dose producing 1 MPD on unprotected skin.||The ability of fabrics to prevent the transmission of UV radiation by absorption and/or reflection and highly dependent on fabric type, porosity, color, weight, thickness, and other factors.|
|Global acceptance||International||United States only||International|
|UV wavelengths protected||UVB||UVA||UVA, UVB|
|Examples||SPF 2 protects against 50% UVB; SPF 8: 88%; SPF 15: 93%; SPF 30: 97%; SPF 50: 98%||UVA-PF1 protects against 20–39% of UVA; PF2: 40–69%; PF3: 70–95%; PF4: >95%a||UPF cotton 5–10; UPF denim 1700|
The quantity and frequency of sunscreen use are the most important factors determining sunscreen efficacy. The international standard quantity of sunscreen application used to determine SPF is 2 mg/cm2.[28, 29] However, Diffey observed that most people apply only 0.5 to 1.5 mg/cm2 of sunscreen and do not reapply sunscreens after swimming or excessive sweating.
Drug-induced photosensitivity reactions occur commonly and are characterized by cutaneous eruptions in sun-exposed areas and result from either toxic or allergic reactions between drugs and UV radiation, primarily UVA.[30-33] Phototoxic reactions are more common than photoallergic reactions, which occur when drug haptens combine with skin proteins producing an immune cellular reaction.
Chronic therapy with certain photosensitizing drugs has been associated with the subsequent development of skin cancers, such as PUVA therapy for psoriasis which increases risks of SCC and CMM.[34, 35] In a retrospective cohort analysis of over 4 million Danes on short- and long-term therapy with other known photosensitizing drugs during the period 1995 to 2006, Kaae and colleagues found that only long-term users of furosemide and methyldopa had a 20% or greater chance of developing BCC and SCC, respectively, with risks increasing with duration of therapy.
Table 2 stratifies some of the more commonly prescribed drugs that can induce photosensitivity reactions by types of reactions and drug classes.[30-33] Many of the medications listed in Table 2 are frequently prescribed for travelers, such as antimalarials, or frequently included in travel first aid kits, such as analgesics. Travelers taking these medications should be warned of the potential risks of drug-induced photosensitivity reactions and encouraged to apply and to reapply high-SPF (30+) sunscreens whenever sun-exposed. The management of photosensitivity reactions includes the identification and future avoidance of the offending drug, which may require photopatch testing, anti-inflammatory dressings and ointments, and topical and/or systemic corticosteroids.[31-33]
|Photosensitivity reaction types||Drug classifications by therapeutic indications|
|Analgesics||Antimicrobials||Cardiovascular drugs||Neurologic/psychiatric drugs||Miscellaneous drugs|
|Some topical antimicrobials|
Some topical sunscreen ingredients:
AvobenzoneCinnamates Ensulizole Oxybenzone PABA derivatives Sulisobenzone
Besides fair-skinned persons, other special populations at increased risks of UV-induced skin cancers include children, organ transplant recipients (OTRs), and persons with sun-sensitive genetic skin diseases.
Epidemiological evidence now supports the observations that children who have suffered repeated sunburns are more likely to develop CMM as adolescents and adults than children who have never had sunburns.[6, 7, 37] In 2012, Gamble and colleagues used ultraviolet photography to examine the relationships between severity of prior sun exposure damage and phenotypic CMM risk factors in children and demonstrated that degree of sun damage correlated with all known CMM risk factors including non-Hispanic Caucasian race, red hair, blue eyes, increased facial freckling, and greater number of nevi (all p values < 0.001). In 2012, Vranova and colleagues reported the results of a case-control study on the risks of prior sun exposures in childhood on the subsequent incidence of CMMs and found the number of sunburn episodes to be significantly associated with CMMs in adolescents and adults.
Epidemiological investigations have now supported associations between UV exposures and NMSCs in immunosuppressed OTRs.[38, 39] In 2009, Terhorst and colleagues assessed the risk factors for NMSCs in OTRs in a survey study that enrolled 70 OTRs who had developed skin cancer after transplantation compared to 69 matched OTRs who had no history of skin cancer. The investigators found the skin cancer group to have fairer skin color than controls (p < 0.05), to have received greater recreational sun exposures (p < 0.05), and to have received a transplant at younger ages (p < 0.001) for longer time periods (p < 0.001) than controls. In addition, the skin cancer group was more likely to have a past or present history of immunosuppression with azathioprine (p < 0.05). In another study, the same group enrolled 120 well-matched subjects in a 2-year prospective case-control study to assess the preventive effects of regular sunscreen use on the incidence of SCC and BCC. At the end of the study, investigators reported that sunscreen users developed no new invasive SCC versus eight in the nonusers, and two new BCC versus nine in the nonusers.
Lastly, patients with two rare genetic skin diseases, epidermodysplasia verruciformis and xeroderma pigmentosum (XP), are also at increased risks of developing UV-associated skin cancers in sun-exposed body sites. XP patients have mutations that inhibit DNA repair following UV-induced DNA damage and demonstrate a significant propensity to develop NMSCs following UV exposures, up to 5,000 times that of the general population.
The intensity of UV radiation is significantly influenced by time of day, season, weather, altitude, latitude, reflective surfaces, degree of shade, and UV transmission through glass.[41-43] In Denmark, a prospective observational study demonstrated that 50% of the total daily solar UV dose reached the earth between 12 am and 3 pm, corrected as indicated for daylight saving times. The average increase in UVB intensity per degree of latitude toward the poles is about 3%.
Travelers enjoying winter mountaineering, skiing, and trekking vacations may be unaware of the necessity to apply sunscreens despite their cold-exposed skin temperatures because of increased UV radiation exposures at high altitudes and UV reflection off snow and ice. At higher altitudes, the atmosphere is thinner, absorbs less UV radiation, and increases the intensity of UV radiation by 4% for every 300 m of higher elevation. Snow can reflect up to 90% of UV light, significantly more than sand (15%–30%) and seawater.
Summertime travelers may also be unaware of increased sun exposures and perceived need to apply sunscreens while swimming and boating because of cooler water temperatures and sea breezes bathing skin surfaces. Swimmers can be exposed to substantial UV radiation in swimming pools by reflection and by direct penetration to depths as great as 1 m.
Although sunscreens are classified for their photoprotective effects by SPF, which primarily represent protection against UVB, photoprotective clothing is classified for its sun protective effects by UV protection factors (UPF), which represent protection against both UVA and UVB. UPFs are influenced by several factors including fabric type, color, weight, porosity or weave thickness/tightness, and even the manner in which the clothing is washed and worn—tight or loose-fitting (Table 3).[45-47] Light-weight fabrics, such as nylon, can be impregnated with UVA- and UVB-absorbing inorganic particles, such as titanium dioxide, that enhance UPF and offer the same cool and light-weight feel of cotton. Popular and inexpensive fabrics well suited for the tropics like cotton can be treated during clothing manufacture with thin layers of titanium or the application of titanium hydrosol with fluorescent whitening agents to enhance UPF and maintain brightness. Some untreated textiles, such as light-weight cotton, offer limited UV protection; while others, such as heavier denim, offer significant protection. Denim has a UPF of 1,700 compared to cotton which has a UPF of 5 to 9. Loose-fitting clothes offer higher UPFs than tight-fitting, stretched, or wet clothing. The UPF is usually higher for materials that are darker in color and have undergone either fabric preshrinkage or fabric shrinkage after having been laundered.
|Physiochemical characteristics||Mechanisms of photoprotection||Recommended selections for travelers|
|Fabric weave||Tightly woven fabrics block UV more than loosely woven fabrics.||Select newer synthetic fabrics with tight weaves.|
|Material composition||Synthetic materials block and reflect more UV than natural materials.||Select nylon and newer synthetic materials.|
|Fabric weight||Thicker and heavier fabrics (denim) block more UV than thinner and lighter fabrics (cotton).||Layer clothing made of lighter synthetic fabrics to increase thickness.|
|Fabric color||Dark-colored fabrics absorb more UV than light-colored fabrics.||Select darker colored sun protective clothing.|
|Fabric fit||Lax materials provide more UV protection than stretched materials.||Avoid tight fitting, stretched clothing.|
|Fabric moisture||Dry materials absorb and reflect more UV than wet materials.||Change out of wet clothing.|
|Shrinkage||Prewashed and preshrunk fabrics provide more UV protection than fabrics labeled “no shrinkage after washing.”||Select prewashed, preshrunk fabrics.|
|Cleaning method||Fabrics labeled dry cleaning only will absorb and reflect more UV than fabrics labeled “home washing permitted.”||Select fabrics that require dry cleaning.|
|Bleach||Unbleached fabrics absorb and reflect more UV than bleached fabrics.||Avoid bleached fabrics.|
|Stain resistance||Fabrics that have been treated for stain resistance absorb and reflect more UV than stain-sensitive fabrics.||Select stain-resistant fabrics.|
|Sunscreen-treated fabrics||Fabrics treated with broad-spectrum UV absorbersa will absorb and block more UV radiation than untreated fabrics.||Select fabrics treated with broad-spectrum UV absorbers.a|
Recently, several photoprotective laundry additives have been developed to enhance the UPF and brightness of frequently washed clothing. Rit Sun Guard® is a photoprotective laundry additive that contains the broad spectrum sunscreen, Tinosorb®, which absorbs both UVA and UVB. Edlich and colleagues have reported that a single laundry treatment of clothing with Rit Sun Guard “sustains a UPF of 30 for approximately 20 launderings.”
Today, photoprotective clothing lines are individually tested and rated for their UPFs which are displayed on the clothing hangtags. The consumer-traveler can gauge the sun protection offered by clothing by reading the UPF on the clothing hangtag with the higher protection factor numbers indicating greater sun protection.
Although sun protective clothing is rated by UPF, hats are rated for their sun protective effects by SPF, adding to consumer confusion. Hats, like sunscreens, are rated for their degree of sun protection by the amount of protection they offer to unprotected head and neck skin from minimal erythema. This degree of protection is principally determined by hat brim circumference and width. Most hats will have SPFs ranging from 0 to 7 depending on their brim circumferences and widths. For example, a hat with a baseball-visor brim that shades the chin (SPF 2) and has a neck-flap (SPF 5) would be assigned a SPF of 7. Hats with 360° brims with brim widths greater than 7.5 cm are highly recommended and will offer greater sun protection to the chin (SPF 2), cheeks (SPF 3), neck (SPF 5), and nose (SPF 7). Adding a neck flap to such a hat would result in an SPF of 22.
Light-weight, titanium-impregnated nylon and cotton fabrics will offer the greatest comfort and sun protection in hot and humid regions and can be layered in cooler and dryer regions. Washing clothing with photoprotective laundering agents, such as Rit Sun Guard, will offer photoprotection through one's favorite clothes at low cost. Besides responsible selection of sun protective clothing, the consumer-traveler should be a responsible wearer of photoprotective clothing by avoiding wet and tightly fitted clothing and gaps of uncovered skin at the ankles, wrists, waist, and neck between the shirt collar and hat.
In addition to wide-brimmed hats and photoprotective clothing, sunglasses also provide photoprotection for the skin and, most importantly, the eyes and eyelids, by preventing the development of several ocular disorders including periorbital skin cancers, cataracts, pterygia, photokeratitis, snow blindness, and possibly retinal melanomas and age-related macular degeneration.[48, 49] There is no world standard UV protection rating system for sunglasses. The first national standard rating system for UV protection for sunglasses was introduced by Australia in 1971. The existing national standard UV protection rating systems for sunglasses are compared in Table 4. Travelers should choose the highest UV protection-rated sunglasses as indicated on the required hangtags.
|Australia||European Union||United States|
|Standard designations||AS/NZS 1067:203||EN 1836:2005||ANSI Z 80.3-2001|
|Transmission ratings||0–4||0–2–6–7||Not applicable|
|Maximum UV filtered (nm)||380||380||400|
|Driving restrictions||Rating 4 only||None||None|
|Handtag label (UV: ultraviolet)||UV 0, 2, 3, or 4||UV 0, 2, 6, or 7||UV 400|
|Source||Standards Australiaa||Requirements of European Directives and Standards Relating to Sunglassesb||American National Standards Institutec|
Sunglass UV protection depends on several factors including shape and fit, and lens color and UV-filtering and reflecting abilities.[48, 49] Sunglass lenses should fit close to the face, not touch the eyelashes, hug the temples, and merge into broad temple arms or straps. Darker lenses do not necessarily filter more UV light and can trigger pupillary dilation which allows unfiltered wavelengths of UV and visible-spectrum blue light (400–440 nm) to reach the retina. Chronic retinal exposure to visible-spectrum blue light in the wavelength range of 400 to 440 nm is a risk factor for age-related macular degeneration.[50-53] The color of sunglass lenses can influence contrast, color vision, and depth and width perception.[50-53] Orange and yellow lenses provide the best protection from both UV and visible blue light, with blue and purple lenses providing insufficient protection.[50-53] The effects of sunglass lens colors on visual perception are compared in Table 5.[50-53]
|Lens color||Contrast||Color distortion||Depth perception||Blue-light protection||Recommendations for travelers in specific activities|
|Blue||No effect||No effect||No effect||None||Not recommended|
|Gray||No effect||None||No effect||None||Elderly drivers|
|Green||No effect||None||No effect||None||Elderly drivers|
|Orange||Increase||Increase||Increase||Good||Boaters, fishers, hunters, pilots, shooters, persons over age 50 years, persons with intraocular lenses|
|Purple||No effect||No effect||No effect||None||Not recommended|
|Red||No effect||None||No effect||Some||Younger drivers|
|Turquoise||Increase||Little||No effect||None||Early AM and late PM use, including driving|
|Yellow||Increase||Increase||Increase||Good||Boaters, fishers, hunters, pilots, shooters, persons over age 50 years, persons with intraocular lenses|
A variety of special use sunglasses are recommended for travelers engaging in active water sports, such as body-boarding, jet-skiing, kite-boarding, wake-boarding, wind sailing, and water skiing. Water sunglasses (goggles) have air vents to prevent fogging and increased buoyancy to prevent sinking if lost. Glacier sunglasses (goggles) provide more UV filtration and reflection and are recommended for travelers engaging in winter and high altitude sports, such as cross-country skiing, downhill skiing, snowboarding, glacier hiking, and mountain climbing.
Special populations at increased risks of UV radiation-induced eye damage include persons older than 50 years and persons who have undergone cataract extractions and intraocular lens insertions. People older than 50 years face increased risks of UV-associated cataracts, pterygia, and eyelid skin cancers. Elderly persons who have had cataracts removed and intraocular lenses placed face increased risks of retinal damage from UV exposures. For additional protection from blue visible light (400–440 nm) not essential for sight, Roberts has recommended that persons over age 50 wear “specially designed sunglasses or contact lenses to reduce the risk of age-related macular degeneration.”
Historically, sunscreens were developed for protection from sunburn from UVB only. Today, most sunscreens are composed of combinations of organic chemicals to absorb UV light (padimate, oxybenzone), inorganic chemicals to filter and reflect UV light (titanium dioxide, zinc oxide), and newer organic particles to both absorb and reflect UV light (Parsol®, Tinosorb®, Uvinul®).
Several factors can significantly affect the protective capabilities of a sunscreen's SPF number including amount of initial sunscreen applied, altitude, season, time of day, sweating, water exposure, UV reflection by snow or water, and skin type. Cool air or water temperatures bathing skin surfaces may influence personal perception of the felt need to apply sunscreens. Cool skin temperatures do not offer UV protection. Sunscreens should be applied to sun-exposed skin throughout the year, even during the coldest seasons, and especially when solar UV radiation can be magnified at altitude or by reflections off ice, snow, or water.
A sunscreen with an SPF of 15 properly applied (defined as 2 mg/cm2 of sun-exposed skin) will protect one from 93% of UVB radiation; SPF 30 is protective against 97% of UVB; SPF 50 is protective against 98% of UVB. Sunscreens should always be broad-spectrum products that block both UVA and UVB rays; and hypoallergenic and noncomedogenic, so as not to cause rashes, or clog pores, causing acne. For children younger than 6 months, always use hats, clothing, and shading, rather than sunscreens. For children older than 6 months, always use photoprotective clothing and sunscreens of SPF 15 and higher depending on skin types.
Reapplications of sunscreens, especially after swimming or excessive sweating, are important practices for vacationing travelers to adopt in high UV index areas.[29, 44] Rai and Srinivas have recommended that individuals should initially apply sunscreens (2 mg/cm2) 30 minutes prior to sun exposures and reapply every 2 to 3 hours thereafter. However, earlier reapplications are indicated following vigorous activities that remove sunscreens, such as swimming, sweating, and towel drying. Using sunscreens labeled as sweat resistant, water resistant, or waterproof are recommended for vigorous activities, and should also be reapplied as follows: (1) 30 minutes after heavy sweating for sunscreens labeled “sweat resistant,” (2) 40 minutes after swimming for sunscreens labeled “water resistant,” and (3) 80 minutes after swimming for sunscreens labeled “waterproof.”
The concurrent applications of commercially available insect repellents and sunscreens are also of special significance for travelers to temperate and tropical areas where both UV exposures and arthropod-borne infectious diseases pose health risks. Although few investigations have studied the potential for adverse effects following concurrent applications of insect repellents and sunscreens, concurrent applications of commercially available insect repellents containing N, N-diethyl-m-toluamide (DEET) and sunscreens containing oxybenzone have been studied in animal models and demonstrated that DEET permeation is potentiated by sunscreens and could promote DEET neurotoxicity, especially in children.[54, 55] According to the American Academy of Pediatrics, insect repellents containing DEET should not be applied to children under 2 months of age, and DEET concentrations ranging from 10% to 30% are recommended for all other children.
As the broad-spectrum sunscreens were designed for their transdermal as well as topical effects, they should be applied prior to the application of insect repellants. Single-product combinations of insect repellents and sunscreens are not recommended by the US Centers for Disease Control and Prevention (CDC) because the instructions for applying sunscreens and insect repellents usually differ. In most cases, insect repellents offer longer protection and do not need to be reapplied as frequently as sunscreens.
Dark-skinned persons are protected from UV radiation by increased epidermal melanin and have significantly lower annual incidence rates of NMSCs. Epidermal melanin in dark-skinned persons filters twice as much UVB radiation as does that in Caucasians. Dark epidermis transmits 7.4% of UVB and 17.5% of UVA rays to the dermis, compared with 24 and 55% in white epidermis, respectively. The six skin types, their definitions, and the recommended SPF for sunscreens appropriately applied by skin type are listed in Table 6.
|Skin type by the Fitzpatrick Scale||Skin color||Skin tone or other common descriptors||Sun exposure effects||Recommended sunscreen SPF|
|I||Pale white||Pale or albino, freckles common|
|Always burns, never tans||30+|
|II||White||Light or fair|
|Always burns, rarely tans||30+|
|Sometimes burns, sometimes tans||15+|
|IV||Light brown||Olive with/without brown tint|
|Tans easily, burns less||15+|
|V||Dark brown||Brown||Tans easily, rarely burns||15+|
|VI||Black||Black||Does not burn||15+|
Randomized controlled trials have demonstrated that regular sunscreen use can prevent the development of AK. As AK is a precursor of SCC, sunscreens can prevent the development of SCC arising in AK. In 1999, Green and colleagues in Queensland reported their results of a 4.5-year community-based randomized controlled trial among 1,621 adult residents of Nambour, a subtropical Australian township in Queensland. Compared to those randomized to using sunscreen at their discretion if at all, study subjects randomized to the daily use of a broad-spectrum SPF 15+ sunscreen showed a 40% reduction in SCC. Although there was no effect on the incidence of BCC during the study period, there was a trend to increasing intervals between BCCs among daily users compared with discretionary sunscreen users who developed multiple BCCs. Eight years after cessation of the 4.5-year sunscreen intervention, participants randomized to the daily sunscreen use group continued to show a 40% decrease in SCC incidence. Their BCC incidence was also 25% lower in the last 4 years of post-intervention follow-up, although not significantly so. At present, the daily use of broad-spectrum SPF 15+ sunscreens appears to have a greater impact on reducing the incidence of SCC than BCC, and this protection from SCC appears to be maintained over time.[61-63]
In 2011, Green and colleagues reported the results of a study designed to evaluate whether the long-term application of sunscreens decreased the risks of CMM in 1,621 randomly selected residents, age 25 to 75 years, in Nambour. Beginning in 1992, study participants were randomly assigned to daily or discretionary sunscreen application to head and arms in combination with 30 mg of beta carotene or placebo supplement until 1996; and then observed by surveys, pathology reports, or cancer registries for CMM occurrences. Ten years after the trial cessation, 11 new primary melanomas had been identified in the daily sunscreen group compared to 22 in the discretionary group (p = 0.051). The reduction in invasive melanoma was even greater with 3 in the daily sunscreen group versus 11 in the discretionary group (p = 0.045). The authors concluded that regular sunscreen use by adults may prevent CMM. Nevertheless, the study of Green and colleagues on CMM prevention by daily sunscreen use prompted an immediate series of subsequent editorials that challenged the external validity of the reported findings as a result of (1) low power to detect significant differences if present, (2) variable interpretations of CMM invasiveness by pathologists, (3) selection of less rigid test statistics, (4) unblinded investigators, (5) exclusions of CMMs on the trunk and extremities, (6) limited application to populations other than light-skinned Australians in Nambour, and (7) the borderline significance of p-values near 0.05.[65-67]
Future double-blinded randomized controlled trials of regular sunscreen use to prevent CMM in larger populations, stratified and matched by several effect modifiers, such as age, gender, skin type, and smoking, will be needed to confirm the findings of Green and colleagues. At present, clinical investigations support the regular use of broad-spectrum sunscreens (1) to prevent the development of AK in sun-exposed subjects, (2) to prevent the development of SCC from new AK in sun-exposed subjects, (3) to possibly prevent the development of CMM in children and adults, and (4) to possibly prevent the development of BCC in OTRs.[38, 39, 60-63]
Observational studies have demonstrated that the public knows little about sunscreen protection, selection, and use, and often misuses sunscreens for intentional solar overexposures. Sunbathing, swimming, skiing, and other outdoor pursuits remain popular activities among travelers despite associations between excessive UV radiation and skin cancer. Some special populations are at high risks of solar UV radiation-associated skin cancers, including children, persons taking certain photosensitive drugs, organ transplant recipients, and persons with rare genetic skin diseases.
Recommended photoprotection strategies for everyone and especially for travelers to high UV index regions should include: (1) practicing responsible sun exposure behaviors, (2) wearing photoprotective clothing, (3) wearing sunglasses, (4) applying broad-spectrum sunscreens, and (5) selecting the right sunscreen for one's skin type. Travel medicine practitioners should always advise their patients to avoid sunburns that could spoil vacations and damage skin and should encourage them to reapply broad-spectrum sunscreens frequently and to wear photoprotective clothing, including broad-brimmed hats. Hotels and resort communities should encourage their guests to adopt responsible sun exposure and protection behaviors by making sunscreens available at swimming pools, tennis courts, golf courses, and all other outdoor venues enjoyed by vacationers. Although the impact of UV radiation on the development of CMM, retinal melanoma, and macular degeneration will require further study, travelers may anticipate future advances in sunscreen composition including the addition of silica-shell microencapsulated UV filters to enhance UV protection, antioxidants to limit DNA damage, and DNA repair stimulants to repair any sun damage.
The authors state they have no conflicts of interest to declare.