Acid mantle

The acid mantle is a very thin, delicate, slightly acidic film covering the entire surface of human skin, serving as a protective barrier against pathogens and reduces body odor.^[1][2] The acidic pH at the skin's surface mainly maintained by free amino acids and α-hydroxy acids (lactic acids) excreted from sweat; free fatty acids and amino acids from sebum; and urocanic acid and pyroglutamic acid.^[3][2] While the viable epidermis below the stratum corneum has a neutral pH of around 7.0, the surface pH of the skin's acid mantle typically ranges between 4.5 and 6.5,^[4][5] with an average assumption of 5.0 to 6.0.^[6]

Formation and maintenance

The acidic pH at the skin's surface is mainly maintained by free amino acids and α-hydroxy acids (lactic acids) excreted from sweat; free fatty acids and amino acids from sebum; and urocanic acid and pyroglutamic acid.^[3][2]

Role

The acid mantle, and its acidic pH, is important for the biological processes that are important for epidermal barrier function.^[3]

Controversy on acidity

Recent research has challenged these proposed ranges, finding that healthy human skin naturally tends to return to acidity levels below 5.0 when left untouched by skincare products or water for extended periods. An ideal pH value of 4.7 has been identified, with some individuals showing levels as low as 4.3. Subjects with a skin pH below 5.0 exhibited significantly less scaling, higher hydration levels, and better skin flora presence compared to those with higher pH levels, suggesting better overall skin condition.^[6]

The acidic surface pH is crucial for the growth conditions of resident skin microbiota, which play a vital role in maintaining skin health. Human skin and its microbiota have a mutually beneficial symbiotic relationship, with the skin providing an optimal environment for resident microbiota while the microbiota help reinforce the skin's immunity by preventing colonization by harmful pathogens and contributing to skin acidification.^[6]

Skin care products that lower skin pH to 4.0–4.5 help maintain resident microbiota on the skin, whereas alkaline personal care products promote their dispersal.^[6]

References

1. Monika-Hildegard Schmid-Wendtner; Korting Schmid-Wendtner (2007). Ph and Skin Care. ABW Wissenschaftsverlag. pp. 31–. ISBN 978-3-936072-64-8. Retrieved 19 June 2012.
2. "Principles of dermatological practice. Structure of the epidermis | DermNet". dermnetnz.org. 3 March 2024. Retrieved 2024-03-10.
3. Kumar, Piyush; Das, Anupam (2023-03-01). "Acid mantle: What we need to know". Indian Journal of Dermatology, Venereology and Leprology. 89 (5): 729–732. doi:10.25259/IJDVL_153_2022. ISSN 0973-3922. PMID 37067107.
4. Zlotogorski A (1987). "Distribution of skin surface pH on the forehead and cheek of adults". Arch. Dermatol. Res. 279 (6): 398–401. doi:10.1007/bf00412626. PMID 3674963. S2CID 3065931.
5. Schmid MH, Korting HC (1995). "The concept of the acid mantle of the skin: its relevance for the choice of skin cleansers" (PDF). Dermatology. 191 (4): 276–80. doi:10.1159/000246568. PMID 8573921. Archived from the original (PDF) on 2011-03-01. Retrieved 2012-06-20.
6. Lambers, H.; Piessens, S.; Bloem, A.; Pronk, H.; Finkel, P. (October 2006). "Natural skin surface pH is on average below 5, which is beneficial for its resident flora". International Journal of Cosmetic Science. 28 (5): 359–370. doi:10.1111/j.1467-2494.2006.00344.x. ISSN 1468-2494. PMID 18489300. S2CID 25191984.