Address correspondence to Dr. Ralf Adam, Procter & Gamble Service GmbH, Schwalbach Technical Center, Sulzbacher Strasse 40, 65823 Schwalbach am Taunus, Germany, or e-mail: firstname.lastname@example.org.
Abstract: The skin of the diaper area has special needs for protection from the irritating effects of urine and feces and prevention of diaper dermatitis. These needs include products such as diapers that absorb the excreta, as well as products for cleansing and conditioning the skin. A number of factors play a role in development of diaper dermatitis, including prolonged exposure to excreta, alterations in skin pH or increased hydration, and changes in skin microbial flora. Recent decades have seen great improvements in our understanding of these factors and our ability to develop new and better products to protect baby skin. Better diaper designs and the development of pH-buffered baby wipes have improved the care of skin in the diaper area. Continuing research offers the promise of new products with additional benefits for caregivers and infants.
As a result of infants’ inability to control urination and defecation, proper hygiene and protection of skin in the diaper area has always been a challenge. Absorbent products such as diapers must be used to absorb the excreta and to facilitate hygiene standards, and extra efforts in skin cleansing and skin care are necessary to maintain skin health. Anatomically, this skin region features numerous folds and creases, which present a problem with regard to both efficient cleansing and control of the microenvironment. During the past 40 years, a range of cosmetic and hygiene absorbent products have been developed especially to address the special requirements for skin care of the diaper region. These products perform well in absorbing waste and cleansing and conditioning skin while demonstrating increasingly good skin compatibility profiles.
A thorough understanding of the anatomy, physiology, and biochemistry of the skin in the diaper area is necessary for the sustainable, targeted development of innovative products that meet caregivers' needs and support infants’ development.
Anatomy of Newborn Skin
The human skin is a remarkable adaptation that allows life on land. Few events in the life of a mammal are as abrupt and dramatic as birth, when the environment of the newborn changes from an aquatic surrounding and maternal oxygen supply to terrestrial exposure and active lung breathing. As is true of other environmental interfaces, the skin experiences a number of changes during the postnatal period as part of the final adaptation to life outside the uterus, including the final stages of structural and functional maturation that began during the third trimester of pregnancy (1). At birth, the skin is covered with the vernix caseosa, a white, cheesy, lipophilic substance that contributes to epidermal maturation in utero and postnatally (2,3). Soon after birth, the stratum corneum of the full-term infant is remarkably capable in fulfilling its key functions, especially that of providing an effective semipermeable barrier between the inside and outside of the body. The anatomy and ultrastructure of the stratum corneum and the epidermis are similar in infant and adult skin. The number of cell layers (approximately 15–20) and overall thickness of the stratum corneum (approximately 15 μm) are comparable in both age groups. The cohesion and adhesion of epidermal cells in newborn skin are not fully developed and thus the connection at the epidermal–dermal junction is weaker than in adult skin. Generally, sebaceous glands occur at a normal frequency but are not yet fully functional in infants, leading to reduced sebum secretion soon after birth. Eccrine sweat gland structure is mature but the number of glands per area unit of skin is higher in the newborn than in adults and the glands primarily serve a thermoregulatory role. Apocrine sweat glands only become functional around puberty.
The skin of premature infants shows signs of immaturity that are dependent in magnitude on the degree of prematurity (4). Histologically, the epidermal development is complete at the 34th week of gestation. The time required to complete postnatal adaptation and reach the skin barrier status of the full-term newborn is dependent on the gestational age of the premature infant at birth and takes from a few hours to several weeks, with more premature infants requiring a longer time (4,5).
Newborns show a different ratio of body surface to body volume or weight, respectively. This fact is, however, currently addressed in guidelines for product safety assessments, which account for individual variations adequately and usually normalize for daily exposure per body weight (6,7).
Physiology of Newborn Skin
The scientific literature reports a series of adaptation processes to the changed environment following birth (8). These changes affect all major biophysical measurements typically used to characterize skin, including trans-epidermal water loss (TEWL), skin hydration, and changes in coefficient of friction, microbial colonization, and pH values of the skin (9,10).
Use of Trans-Epidermal Water Loss Measurements
Diaper area TEWL values have been widely generated during the past 15 to 20 years. The published literature needs to be read carefully, as the circumstances of the measurements, such as providing appropriate environmental control and sufficient equilibration time, are not always consistent with the international guidelines (11). It is also important to consider whether the TEWL measurements were used to determine the barrier status of the diapered skin per se (12,13) or to determine the capability of a diaper to keep the skin dry, i.e., to measure a skin surface water loss (SSWL) (14). Most authors report newborn skin TEWL values that are lower than or equal to the values obtained for adult skin. In the immediate postnatal period, lower TEWL values can be attributed to the presence of the vernix caseosa, which provides an additional barrier for epidermal water loss (15,16). Visscher et al (17) found small but significant differences in TEWL values in the diaper area after an equilibration time of up to 18 minutes. The sharp decline compared with the SSWL values 3 minutes after opening the diaper, however, might indicate that the skin did not fully adapt to the environmental conditions. The ability of skin to provide an effective barrier is clearly dependent on gestational age and functional as of approximately 34 weeks (4,5).
Role of Skin Hydration
Hoeger and Enzmann (9) investigated statum corneum hydration at different anatomic locations in infants aged from 3 days to 12 weeks. While they found an overall increase in skin hydration, no difference was measured between anatomic sites, including the buttocks area. Consistent with those results, Giusti et al (15) found capacitance values on forearms higher than on buttocks. A series of diaper studies conducted mainly in the late 1980s found a significant decrease in skin hydration following the introduction of diapers with a superabsorbent core. Recent studies confirm that this trend is ongoing (13).
Microbiology of the Diaper Area
The microbiology of the diaper area has been investigated mainly in the context of general hygiene, the involvement of microorganisms in diaper rash and the influence of skin cleansing formulations, specifically their pH, on the microflora of the skin. One main purpose of diapers is to contain the excreta and prevent contamination of the outer clothing and environment. The superabsorbent material in modern products rapidly absorbs body fluids and efficiently locks them away. The outer sheet of these products is made of a waterproof material that ensures effective containment of the excreta. Elastic materials in diapers such as the leg bands and leg-cuff barriers help to prevent leakage. Clinical studies have shown that the chance of spread of fecal contaminants is greater during use of cloth diapers than disposable diapers (18). Storing and handling soiled cloth products increases the potential for contamination and spread of infections in the household and in the environment, especially in developing countries (19).
The microorganism mainly associated with severe instances of diaper rash is Candida albicans. It has been shown that modern diaper technologies can contribute to keeping Candida in the diaper area under control (20). A series of studies has shown that the pH of cleansing products can change the microbiological spectrum of the skin. High soap pH values encourage propionibacterial growth on skin whereas syndets (i.e., synthetic detergents) with a pH of 5.5 did not cause changes in the microflora (21).
Stratum corneum acidification is described as a necessary prerequirement to ensure normal stratum corneum barrier homeostasis, since it not only protects the skin from certain microorganisms but also ensures pH-dependent lipid processing and formation of functional lipid lamellae (22,23). The normal skin pH is acidic and reported to range from approximately 4.5 to 6.0. At birth, the skin pH of full-term neonates is above 6.0 and is reported to normalize within a few days after birth (3,9,15,16). Among other factors, this increased pH might still reflect the influence of the vernix caseosa (pH 7.4) and the amniotic fluid (pH 7.15) (24). The pH values in atopic infants and infants with ichthyosis are reported to be significantly higher, even in the postnatal period, which could indicate a role of pH for an intact lipid turnover and barrier function (25).
The postnatal development of skin pH is determined by exogenous components such as lactic acid, eccrine sweat, and free fatty acids derived from sebaceous gland lipids (26). Skin pH is also largely determined via metabolic pathways such as the generation of free fatty acids from phospholipids via enzymatic activity of phospholipases A2 (27), urocanic acid via enzymatic degradation of histidine, pyrrolidone carboxylic acid, and Na+/H+ isoform 1 (NHE1) (22,28,29). Products associated with the desquamation process of the stratum corneum, such as breakdown products of filaggrin and keratohyalin, have been reported to contribute to skin pH. The outer skin surface pH, however, is not representative of the pH value across the stratum corneum. The stratum corneum pH changes dramatically by 2 to 3 pH units in less than 20 μm of tissue. This pH gradient (22,30) is essential for
• Stratum corneum differentiation and barrier repair, which depends on pH-dependent enzymatic activity (e.g., β-glucocerebrosidase and acidic sphingomyelinase (29–31));
• Synthesis of ceramides, which requires pH-dependent enzyme activation (32); and
• Equilibrium of desquamation and cell cohesion, which depends on regulated functions, e.g., the actions of cathepsin D and chymotryptic serine protease (33).
Skin Care in the Diaper Zone and Infant Care Products
Impact of Diapers
Skin care in the diaper area needs to be considered in a broad sense, addressing containment and hygienic cleaning aspects as well as cosmetic skin care and aesthetic issues. To address these needs, diaper changes can employ a wide variety of cleansing implements, immersion bathing, application of lotions, creams, ointments and powders. The habits and practices of caregivers show significant variability and depend on culture, social status, beliefs, and often, emotional aspects. Those regional differences can include professional settings (34).
Diaper rash or irritant diaper dermatitis is a nonspecific medical term that describes a spectrum of symptoms in the diaper area caused by inflammatory skin reactions. It is still a general opinion among the dermatologist community that diaper rash occurs regularly (35), although overall incidences and severities have declined. An analysis of our clinical studies conducted during the mid-1980s to mid-1990s supports this opinion (Fig. 1).
Published clinical and laboratory model studies demonstrate the etiologic factors for diaper rash. Those factors include skin wetness, biochemical irritants, and an increased pH as a consequence of skin exposure to excreta (36) (Fig. 2). Exposure of urine to feces causes the formation of ammonia via degradation by the ureases of fecal microbes. The resulting pH increase can reactivate fecal proteases and lipases, and thus lead to attack of the corneocyte proteins and interstitial lipid lamellae of the stratum corneum (37), which results in an impaired barrier function. Hydrated skin is also more prone to mechanical damage and chafing of the skin as it shows an increased coefficient of friction and may allow irritants to penetrate the stratum corneum more easily. These observations contributed to the understanding that good control of skin wetness and pH are critical for maintaining skin health in the diaper area.
A century ago, diapers were made primarily of woven textiles fabrics such as cotton or wool. To prevent leakage and control containment, some impregnated outerwear, e.g., wraps soaked with wax, were used. The fabrics were often in triangular shape and needed to be folded and wrapped around the diaper zone. Subsequently, inner liners were developed to provide a higher capacity. In the middle of the last century, diapers were made from cotton and fixed with pins. Waterproof rubber pants were used as outerwear. Early disposable diapers contained a poly backsheet film, a fluff pulp core, and a separate removable topsheet that could be discarded with the feces.
In the 1970s and 1980s, the rectangular diaper shape changed to some die-cut shapes with leg cuffs. Most importantly, superabsorbent polymers were introduced and mixed with fluff pulp to build the diaper cores. Elastic barrier leg cuffs were developed to further improve leakage performance. Modern fastening technologies evolved from plain adhesive tapes to the addition of hook and loop fasteners that allow opening and reclosing even when the caregiver’s hands are contaminated with lotion or creams.
Recently, very dynamic innovations in the area of superabsorbent polymers allow a more efficient use of raw materials and the development of increasingly thinner, underwear-like diapers. Today, specific diapers are available for infants of different developmental stages that take the concomitant physiologic changes into account. These new products were characterized by increased speed of liquid acquisition and higher absorbent core capacity, resulting in increased skin surface dryness (Fig. 3).
The use of lotioned inner topsheets is an elegant approach to the care of infant skin by ensuring the ongoing application of a small amount of a petrolatum-based ointment. This ointment provides an efficient skin barrier without occluding the skin (12,13). The cosmetic barrier treatment also facilitates easier cleaning of the skin, leaving less residual fecal material and thus fewer potential irritants on skin. The newest developments in diapers include a topsheet with small openings and an underlying corrugated structure to trap feces in the diaper core.
Impact of Cleansing Regimens
Cleansing products can interfere with the diaper rash cycle by removal of skin contaminants, restoration of the physiologic skin pH value, and deposition of effective skin care active ingredients. In the professional world, water and wash cloth are often seen as the golden standard for cleansing. It should be recognized, however, that the polar nature of water limits its ability to remove lipophilic substances from the skin and that water is incapable of any pH buffering action. Consequently, water can negatively impact skin physiology over time (38–40) and does not provide an advantage over other cleansing methods, such as use of infant wipes, in a clinically controlled setting (41). In addition, some implements such as wash cloths or sponges can be a challenge for efficient hygiene if reused and can cause skin irritation resulting from friction and mechanic abrasion, especially if the skin is already compromised.
During the last decade, disposable infant wipes have been developed as a valid alternative to traditional cleansing methods such as wash cloths or other cleaning implements with water or water and soap. Modern infant wipes usually consist of a nonwoven carrier, which is soaked with an emulsion-type watery or oily lotion. Ideally, the fibers are woven via a process called hydro-entanglement, which eliminates biocidal use in chemical binders. The lotions used in Europe today either contain more than 90% water, often using different emulsion technologies, or consist purely of mineral oils.
The emulsion-type lotions are often enriched with emollients and surfactants and may contain different skin care additives and fragrances. As they are water-based, a preservative system is added to ensure that the product will not be contaminated during use, when caregivers regularly enter the wipes pack with potentially feces-contaminated hands. Several manufacturers have developed products specifically for sensitive skin. Consumers may now choose products on the basis of fragrance or added skin care additives such as chamomile, aloe, or panthenol.
Mineral oil wipes may not be able to efficiently clean hydrophilic components from the skin and may slip over fecal contaminations. Also, care must be taken to avoid skin occlusion from high levels of oily substances.
The available skin compatibility data for infant wipes demonstrate the mild nature of products on the market (41,42). Generally, those reports demonstrate skin mildness of wipes that is as good or better than that for the use of water and a wash cloth (Fig. 4).
The products had been shown to be suitable for use also on compromised, irritated skin, on newborn infants and on an atopic population. Efficient pH buffering systems offer an opportunity to stabilize skin pH at physiologic levels and thus help to overcome the potentially detrimental effects of an elevated skin pH in the diaper area. Barel et al (43) rightly point out the importance of buffering capacity in this respect to obtain sustainable and stable skin effects. Bechor et al (44) found a clear correlation between the mean change in skin pH after washing and the necessary recovery time back to normal levels, which stresses the need for cleaning practices which are capable of sustainably maintaining the physiologic skin pH value. Fluhr et al (45) demonstrated the importance of the stratum corneum pH gradient for barrier homeostasis. The barrier function of stratum corneum could be improved via topical application of an acidic buffer.
Soaps, Cleansers, and Bubble Baths
Soaps are defined as alkali salts of fatty acids. Usually, their skin compatibility is determined by the carbon chain length of the fatty acid itself. Classic soaps have a high pH value around 10 and can have a sustained negative pH impact on skin. The calcium and magnesium salts of soaps are minimally water-soluble and can leave irritating precipitates on skin (38,43,44,46).
Syndets (synthetic detergents) are nonsoap surfactants, which are often derived from cocoyl isethionate or sulfosuccinates, alkyl sulfates, and betaines (Table 1). DiNardo et al (47) reported an inverse relationship between surfactant skin reactivity and the amount of ceramides in the stratum corneum. This was attributed to a potential delipidization effect of the surfactants (40,48). Petrolatum additives or rice starch might be alternative additives to bubble baths and cleansing preparations to prevent a potential delipidization and the skin drying effect of surfactants (49,50).
Often used in liquid preparations; stable foam and creamy lather, less effective in hard water; epidermal permeability depends on C-chain length
Good lather characteristics can be used as rheology modifiers
Alkylglucosides, fatty acid alkanolamides
Creams, Lotions, and Ointments
Oil in water and water in oil preparations as well as lipid ointment preparations are frequently used in the diaper area; many of these preparations contain zinc oxide as an active skin recovery ingredient. In Europe, chamomile/bisabolol, aloe barbadensis, and different dimethicones or dexpanthenol are often added for skin recovery and barrier properties. Glycerine is frequently used as a moisturizer and tocopheryl acetate as an antioxidant. Hydrophilic preparations have been described to be limited in their barrier properties in the diaper zone (35).
Petrolatum-based preparations have been shown to be effective to support skin barrier function (12,50), even in premature infants (51). Over the counter creams containing antiseptics should be used only in severe cases, such as instances of C. albicans involvement in which antifungal preparations may be used as advised by the pediatrician.
Although the etiology of diaper rash and its contributing factors are well understood (36), a considerable number of irritations are still observed in the diaper area. Further innovative product development should focus on maintenance of natural skin physiology, such as skin dryness and skin pH, via corresponding features in diapers and wipes. This includes further physical or chemical separation of excreta from skin by diapers and stabilization of skin pH by increased buffering capacity of wipes lotions.
The author acknowledges Edburga Krause, Baerbel Schnetz, Geetha Erasala, and Harald Schlatter for helpful discussions and Lisa Bosch for excellent help in reviewing the manuscript.