Efficacy of ceramide‐containing sunscreen on skin barrier

UV rays not only cause oxidative damage to the skin, but also damage its barrier function. The use of sunscreen is crucial in preventing skin from UV radiation, but it may have an impact on the function of the skin barrier. While much research has focused on the protective effects of sunscreen against UV oxidative damage, little is known about the impact of daily sunscreen use on the skin barrier.

UV radiation can enhance the skin barrier function, but acute overexposure can damage to skin barrier, resulting in symptoms such as erythema, edema, blisters, and inflammatory pain. 2 Skin barrier damage may be indicated by an increase in TEWL, a decrease in water content, and an increase in erythema index.Furthermore, our previous research has shown that exposure to high levels of UV can lead to a reduction in skin barrier proteins and ceramides, which covalently bind to corneocytes, resulting in damage to the skin's brick-and-mortar structure. 3,4nscreen is currently one of the best ways to protect against UV radiation.In the past, research has mainly about sunscreen focused on maximizing UV absorption, prevent skin from photodamage or skin cancer, and developing sunscreens that are safe for coral reefs. 5,6For example, regarding the safety concerns for corals, some researchers are developing sunscreen formulations that combine known coral-friendly ingredients(e.g., ZnO and Diethylamino Hydroxybenzoyl Hexyl Benzoate) to explore both highly efficient sun protection performance and coral-friendly properties. 7 the other hand, other researchers are also exploring the development of new polymeric UV filter because their larger molecular size makes it difficult to penetrate the skin and corals, thus exhibiting mild characteristics towards both human beings and corals. 8However, there has been little research on the relationship between sunscreen and the skin barrier.Many consumers in China even worry that using sunscreen products may burden or damage the skin barrier. 9 previously conducted a systematic study on the damage caused by UV radiation to the skin barrier, 4 and further demonstrated that ceramide-containing sunscreen not only protects against direct damage from UV radiation but also repairs barrier damage in ex vivo and in vivo models. 4,10In this clinical study, we delve deeper into the alterations in skin barrier function resulting from the daily application of sunscreen products containing ceramides, with the aim of simulating typical daily usage habits of sunscreen.

| MATERIAL S AND ME THODS
The study was conducted in a group of 60 Chinese women (mean age 36.43 years) recruited through advertising and electronic media.Forty people self-reported sensitive skin in panels.Exclusion criteria were as follows: facial sun damage (dyschromia) or other skin diseases such as psoriasis, rosacea, acne, and eczema; history of allergy to facial care products; currently pregnant, or planning to become pregnant; suffering from heart, brain, lung, liver, or kidney diseases; as well as patients who were uncooperative or had incomplete information were excluded from the study.All subjects were informed and gave their consent before enrollment.
The treatment sunscreen contains both UV filter including 3% avobenzone, 10% homosalate, 5% octisalate, 2.7% octocrylene, and more importantly ceramide 1,3,6.According to a predetermined randomization table, one Tewameter measurement will be taken at the center of either the right or the left cheek of each subject.
Three Mexameter measurements will be taken at the same location as the Tewameter measurement (at the center of either the right or the left cheek) for each subject.
Three Corneometer measurements will be taken for each subject at the center of either the right or the left cheek, opposite to the side where the Tewameter measurement was taken.
In addition, after 1 and 4 weeks of product use, the volunteers were assessed for adverse reactions by the physician.

| Statistical analysis
The changes in each parameter after use were calculated by subtracting the post-use measurement from the pre-use measurement.
The paired t-test or Wilcoxon signed-rank test was used to test the null hypothesis that the mean change value before use was zero.Statistical analysis was performed using SPSS 28.0 with a significance level of α = 0.05 and a two-tailed test.

| Skin a*
Compared to before using the sample, after using the sample for 1 week, there was a significant reduction of 10.96% in skin redness as measured by a* value, and 82% of subjects showed improvement.
After using the sample for 4 weeks, there was a significant reduction of 11.89% in skin redness as measured by a value, and 87% of subjects showed improvement (Figure 1).

| Skin EI
Compared to before using the sample, after using the sample for 1 week, there was a significant reduction of 5.63% in skin hemoglobin content, and 77% of subjects showed improvement.After using the sample for 4 weeks, there was a significant reduction of 5.68% in skin hemoglobin content, and 83% of subjects showed improvement (Figure 2).

| Skin TEWL
Compared to before using the product, after 1 week of product use, there was no significant reduction in transepidermal water loss (TEWL), but 57% of subjects showed improvement.
After 4 weeks of product use, there was a significant reduction of 22.96% in TEWL with 97% of subjects showing improvement (Figure 3).

| Skin hydration
Compared to before using the product, after 1 week of product use, there was a significant increase of 15.34% in moisture content of the stratum corneum with 92% of subjects showing improvement.After 4 weeks of product use, there was a significant increase of 21.96% in moisture content of the stratum corneum with 97% of subjects showing improvement (Figure 4).

| DISCUSS ION
Different exposure times to sunlight have varying effects on skin wrinkles, color, moisture content, sebum production, and so on. 11ere is a limited amount of research on the impact of sunscreen use on skin homeostasis, and little studies have compared skin homeostasis parameters before and after applying sunscreen.While there have been studies on the effects of sunscreens on TEWL, these have mostly focused on sunscreen use during physical exercise. 12th a* and erythema exhibit a reduction following sunscreen application.They directly reflects the situation of blood hemoglobin in the dermal papillary layer.An increase in these indexes indicate that the skin's vascular reactivity is higher and serve as reliable markers for the impact of irritants on the skin, given their association with inflammation. 13In previous studies, four different sunscreens without ceramides did not improve TEWL values. 15On the contrary, in our study the data supported a notable improvement in facial TEWL index.This suggests that ceramides play a significant role in repairing UV-induced skin damage.As our previous study shows, topical application of ceramide-containing suncare products help maintain SC essential ceramide subclasses and proper ceramide chain length in ex vivo model. 3in capacitance, or SCH, is another significant indicator of skin health, and abnormally low levels are often indicative of compromised skin-barrier function. 16Our results also indicated a significant improvement in facial hydration.
There are several limitations to our study.The sample size could be expanded to enhance the statistical power of the findings.In addition, the study only measured physiological parameters of the skin and did not assess molecular levels (including FLG expression and ceramide expression).In the future, we can further explore the different effects of sunscreen with and without ceramide on the skin.Additionally, lipidomics, and proteomics can be used to investigate the changes in the skin resulting from daily use of ceramidecontaining sunscreen.

| CON CLUS ION
Daily application of ceramide-containing sunscreen can increase skin hydration while enhancing the function of the skin barrier.

CO N FLI C T O F I NTE R E S T S TATE M E NT
We declare that we have no conflict of interest.And all authors have read and approved the final manuscript.
Skin parameters were measured at baseline, after 1 and 4 weeks of test product use in a single-blinded fashion.In vivo skin parameters were evaluated as follows: Using IPP software to analyze the a* values of the cheek left or right AOI (area of interest) in the RBX-Red illumination mode side view images of each subject captured by VISIA CR according to the predetermined randomization table.The analysis area of each image should remain constant for each subject at each time point.

F I G U R E 1
Skin a* value change after using the sunscreen.F I G U R E 2 Skin EI value change after using the sunscreen.F I G U R E 3 Skin TEWL change after using the sunscreen.F I G U R E 4 Skin hydration change after using the sunscreen.Trans-epidermal water loss (TEWL) is a crucial parameter that reflects the integrity of the skin barrier.Research has consistently demonstrated that increased TEWL values are closely linked to impaired skin-barrier function, while lower TEWL values indicate healthier skin.
Cao:Main author, responsible for clinical evaluation and consultation.Xianghua Zhang: Responsible for the development and consultation of the clinical evaluation form; contributed to cosmetic efficacy testing and paper editing.Xiaofeng He: Contributed to cosmetic efficacy testing and paper editing; main developer of the self-report part of the consumer questionnaire.Wenna Wang: Contributed to cosmetic efficacy testing and paper editing; leader and consultant of the equipment testing part.Yi Yi: Responsible for the safety evaluation and consultation of product safety and tolerance, contributed to paper editing.Yunfei Ai: the initiator and sponsor of the research; responsible for the development of research proposal, etc.