What is the Acid Mantle of Your Skin Barrier? How Does it Protect You?

Posted by Dr. Natasha Ryz on

  What is the Acid Mantle of Your Skin Barrier?

The term "acid mantle" describes the inherent acidic nature of the outer skin barrier, or stratum corneum.

Maintaining skin pH is important, as skin pH influences skin barrier homeostasis, stratum corneum integrity and cohesion, and antimicrobial defense mechanisms. 

Many factors can affect the pH of the skin, including age, sebum, sweat, detergents, cosmetics, and irritation.

Why is the Acid Mantle Important?

In 1928, the physicians Heinrich Schade and Alfred Marchionini first coined the term Säuremantel or “acid mantle” to describe the inherent acidic nature of the outer skin barrier, or stratum corneum (Schade et al, 1928).

The pH of the skin is slightly acidic, in the range 4.5 to 6.5.

The low pH level is maintainted by fatty acids, sebum and sweat (Chan et al, 2011).

In the skin, pH level plays a key role in maintaining proper skin barrier function, control of desquamation (shedding skin cells) and protection against pathogens (reviewed by Ali et al, 2013).

Skin pH maintains skin barrier

Several key enzymes involved in the synthesis and maintenance of the skin barrier are largely impacted by pH, especially with respect to its lipophilic components and its destruction by desquamation. These hydrolases include -glucocerebrosidase, acid sphingomyelinase, acid lipases, phosphatases and phospholipases (Schmid-Wendtner et al, 2006).

For instance, the enzyme glucocerebrosidase with an optimum pH of 5.6 is involved in the synthesis of the most important ceramides (Schmid-Wendtner et al, 2006).

Ceramides are fats or lipids that are found in skin cells. They make up 30% to 40% of your outer skin layer, or epidermis. Ceramides are important for retaining your skin’s moisture and keeping your skin barrier healthy.

Skin pH protects against bad bacteria

For the skin's antimicrobial defence, there is an association between a lower pH level and reduced expression of bacteria proteins, in particular, those involved in adherence to the skin by bacteria Staphylococcus aureus (e.g., protein A, clumping factor B, fibronectin-binding protein A) (Leung et al, 2013).

High Staphylococcus aureus colonization rate is shown in children and adults with atopic dermatitis (eczema). Colonization rate increases with the severity of the atopic dermatitis, and it acts as an aggravating factor exacerbating inflammation (Ogonowska et al, 2021).

Changes in the pH level toward more alkaline are one of the factors, facilitating Staphylococcus aureus colonization and growth in patients with atopic dermatitis (eczema) (O'Regan and Irvine, 2008; Proksch et al, 2008; Clausen et al, 2019). 

A higher skin pH 7.0–8.0 has been shown optimal for Staphylococcus aureus sticking to human skin cells (Mempel et al, 1998).

What is the Skin Barrier?

The skin barrier includes the outermost layers of skin, called the stratum corneum.

Your skin barrier is essentially what you can see and touch on the surface of your body.

When your skin barrier is healthy, it feels and appears smooth, soft, and plump.

In contrast, a damaged skin barrier looks dry, rough, dull, and dehydrated, and may become irritated and inflamed.

Our skin is the primary barrier from the outside environment- it protects us from injury, water loss, UV radiation and invasion from microbes and toxins.  

Learn more: What is the Skin Barrier?

What is your skin barrier? How does it affect dry skin care?
What is the Stratum Corneum? "The brick wall"

The stratum corneum is the most outer layer of your skin.

The stratum corneum can be thought of as a brick wall that protects you.

The "bricks" are the skin cells, called corneocytes, and the "mortar" that holds the bricks together is the lipids or fats, that together create the outer barrier.

What is the Stratum Corneum made of?

The stratum corneum is composed of skin cells, water, and lipids.

On a weight basis, the stratum corneum contains approximately 70% protein, 15-25% water and 15% lipids (Ananthapadmanabhan et al, 2013).

There are approximately 15 to 30 layers of corneocytes in the stratum corneum.

What are Corneocytes? "The bricks of the wall"

"The bricks of the wall" are corneocytes, skin cells that compose most if not all of the stratum corneum.

Corneocytes are terminally differentiated from skin cells called keratinocytes, which populate the lower levels of the skin barrier.

What is the Skin Barrier? Stratum Corneum

Corneocytes are regularly replaced through desquamation and renewal from lower epidermal layers, making them an essential part of the skin barrier property.

Cell Turnover and Loss

Desquamation is the natural process of shedding skin cells.

New skin cells are formed at the base layer of the skin, and they differentiate and migrate towards the skin surface, in a process that takes approximately 30 days. Nearly a billion cells are lost each day from the surface of adult skin (Milstone et al, 2004). 

What are Keratinocytes?

Keratinocytes are the major cell type in the epidermis, and make up 95% of the cell population. Keratinocytes are formed at the basal layer just above the dermis. They are metabolically active cells with normal constituents such as a nucleus and cytoplasm.

As keratinocytes mature, they differentiate into corneocytes, which serve as a physical barrier, and protect your body from the external environment.

What are Corneocytes made of? Proteins, AAs and NMFs

Corneocytes are mostly made up of the protein keratin, which is also found in hair and nails.

Corneocytes in the stratum corneum are filled with keratin filaments as well as amino acids (AAs) and other small molecules, collectively referred to as natural moisturizing factors (NMFs), derived from the breakdown of filaggrin, a protein that surrounds the keratin filaments (Verdier-Sévrain et al, 2007).

What are Natural Moisturizing Factors (NMFs)?

Natural moisturizing factors (NMFs) are a mix of humectants or hydroscopic molecules that help attract and hold onto water and maintain hydration in the skin.

Natural moisturizing factors (NMFs) include amino acids and their derivatives (pyrrolidone carboxylic acid and urocanic acid) made from the breakdown of epidermal filaggrin. Other components found within but also external to the corneocytes include lactates, urea, and electrolytes

Natural moisturizing factors (NMFs) are present in high concentrations within corneocytes and represent up to 20% to 30% of the dry weight of the outer skin layer (Verdier-Sévrain et al, 2007). 

Learn More: What is Dehydrated Skin?

Lipids "The mortar that holds the bricks together"

Epidermal lipids are are a mixture of ceramides, free fatty acids and cholesterol. These lipids are released from skin cells and fill the spaces between the cells, like mortar or cement (Pappas, 2009).

The stratum corneum lipids consist of an equimolar mixture of ceramides (45–50% by weight), cholesterol (20–25%), and free fatty acids (10-15%), with lower quantities of cholesterol sulfate and nonpolar lipids (Verdier-Sévrain et al, 2007).

Learn More: Beneficial Fats Found in Your Skin Barrier

What is the Acid Mantle?

The acidic pH is the result of keratinocyte-produced free fatty acids, and components of natural moisturizing factors (NMFs), including urocanic acid, carbonic acid, and keratins  (Schmid-Wendtner et al, 2006). 

The pH of the extractable water-soluble components of the skin can be measured. The skin pH and the buffering capacity of the skin surface are made up of the contributions from all the components of the stratum corneum as well as the secretions from sebaceous and sweat glands (Dikstein et al, 1994).

What does pH stand for?

In chemistry, pH denoting 'potential of hydrogen' or 'power of hydrogen' is a scale used to specify the acidity or basicity of an aqueous solution. Acidic solutions (solutions with higher concentrations of H+ ions) are measured to have lower pH values than basic or alkaline solutions.

The letters pH stand for potential of hydrogen, since pH is effectively a measure of the concentration of hydrogen ions (that is, protons) in a substance. The pH scale was devised in 1923 by Danish biochemist Søren Peter Lauritz Sørensen (1868-1969).

What is the pH of skin?

The pH of the skin is generally in the range 4.5 to 6.5.

pH numbers refer to the acid, neutral or alkaline nature of the skin. The number is a range from 1 to 14, where 1 is highly acidic and 14 is highly basic (or alkali).

The pH at the surface of healthy adult human skin is slightly acidic, around pH 5 (Schade et al, 1928; Lambers et al, 2006).

A proper skin pH is important to maintain healthy skin conditions, cutaneous homeostasis (Flur et al, 2002, Rippke et al, 2002; Parra et al, 2003; Hachem et al, 2003) and microbial flora (Leyden et al, 1987, Lambers et al, 2006).

What can affect skin pH?

Many factors can affect the pH of the skin, including age, sebum, sweat, detergents, cosmetics, and irritation (Ali et al, 2013; Yosipovitch et al, 1996).

Even rinsing your skin with water alone produces an immediate but transient increase in its pH (Gfatter et al, 1997). 

The High pH of Soap Can Disrupt Your Skin Barrier

Soaps typically have a high pH of 9-10, and soap can disrupt your skin barrier.

The pH of the skin is generally in the range 4.5 to 6.5.

The high pH of soap causes swelling of the stratum corneum, which allows unwanted deeper penetration of the soap into the skin possibly causing irritation and itching (Prottey et al, 1975).

Soap can also binds to stratum corneum proteins further inducing swelling and hyper hydration of the skin. Following the completion of washing, the excess water evaporates leading to skin tightness and dryness because the soap binding reduces the ability of the skin proteins to hold water. This explains the reduction in skin hydration and elasticity following soap cleansing (Draelos et al, 2018).

Learn More: 8 Types of Face Cleansers - Which Are Best for Cleansing Your Dry Skin?

Summary

The skin barrier, or stratum corneum can be thought of as a brick wall that protects you.

The pH of the skin barrier is slightly acidic, in the range 4.5 to 6.5.

The term "acid mantle" describes the inherent acidic nature of the outer skin barrier, or stratum corneum.

Maintaining skin pH is important, as skin pH influences skin barrier homeostasis, stratum corneum integrity and cohesion, and antimicrobial defense mechanisms. 

Many factors can affect the pH of the skin, including age, sebum, sweat, detergents, cosmetics, and irritation.

Soaps and cleansers that are high in pH should be avoided, as high pH soaps can irritate and disrupt the skin barrier.

References:

Ali SM, Yosipovitch G. Skin pH: from basic science to basic skin care. Acta Derm Venereol 2013; 93: 261–267. 

Ananthapadmanabhan KP, Mukherjee S, Chandar P. Stratum corneum fatty acids: their critical role in preserving barrier integrity during cleansing. Int J Cosmet Sci. 2013 Aug;35(4):337-45. 

Chan A., Mauro T. (2011). Acidification in the epidermis and the role of secretory phospholipases. Dermatoendocrinology 3 84–90. 

Clausen M. L., Edslev S. M., Nørreslet L. B., Sørensen J. A., Andersen P. S., Agner T. (2019). Temporal variation of Staphylococcus aureus clonal complexes in atopic dermatitis: a follow-up study. Br. J. Dermatol. 180 181–186.

Dikstein S, Zlotogorski A: Measurements of skin pH. Acta Derm Venereol (Stockh) 1994;(suppl 185):18–20.

Draelos ZD. The science behind skin care: cleansers. J Cosmet Dermatol. 2018 Feb;17(1):8-14..

Gfatter R, Hackl P, Braun F. Effects of soap and detergents on skin surface pH, stratum corneum hydration and fat content in infants. Dermatology 1997; 195: 258–262.

Hachem JP, Crumrine D, Brown BE, Feingold KR, Elias PM. pH directly regulates epidermal permeability barrier homeostasis, and stratum corneum integrity/cohesion. J Invest Dermatol 2003; 121: 345–353.

Lambers H, Piessens S, Bloem A, Pronk H, Finkel P. Natural skin surface pH is on average below 5, which is beneficial for its resident flora. Int J Cosmet Sci 2006; 28: 359–370.

Leung D. Y. M. (2013). New Insights into atopic dermatitis: role of skin barrier and immune dysregulation. Allergol. Int. 62 151–161.

Leyden JJ, McGinley KJ, Nordstrom KM, Webster GF. Skin microflora. J Invest Dermatol 1987; 88: 65s–72s.

Mempel M., Schmidt T., Weidinger S., Schnopp C., Ring J., Abeck D., et al. (1998). Role of Staphylococcus aureus surface-associated proteins in the attachment to cultured HaCaT keratinocytes in a new adhesion assay. J. Invest. Dermatol. 111 452–456. 

Milstone LM. Epidermal desquamation. J Dermatol Sci. 2004 Dec;36(3):131-40.

Ogonowska P, Gilaberte Y, Barańska-Rybak W, Nakonieczna J. Colonization With Staphylococcus aureus in Atopic Dermatitis Patients: Attempts to Reveal the Unknown. Front Microbiol. 2021 Jan 11;11:567090.

O’Regan G. M., Irvine A. D. (2008). The role of filaggrin loss-of-function mutations in atopic dermatitis. Curr. Opin. Allergy Clin. Immunol. 8 406–410.

Pappas A. Epidermal surface lipids. Dermatoendocrinol. 2009 Mar;1(2):72-6.

Parra JL, Paye M. EEMCO Group. EEMCO guidance for the in vivo assessment of skin surface pH. Skin Pharmacol Appl Skin Physiol 2003; 16: 188–202. 

Proksch E., Brandner J. M., Jensen J. M. (2008). The skin: an indispensable barrier. Exp. Dermatol. 17 1063–1072.

Prottey C, Ferguson T. Factors which determine the skin irritation potential of soaps and detergents. J Soc Cosmetic Sci. 1975;26:29- 46.

Rippke F, Schreiner V, Schwanitz HJ. The acidic milieu of the horny layer: new findings on the physiology and pathophysiology of skin pH. Am J Clin Dermatol 2002; 3: 261–272. 

Schade H, Marchionini A. Der s€auremantel der haut (nach Gaskettenmessung). Klin Wochenschr 1928; 7: 12–14. 

Verdier-Sévrain et al. (2007). Skin hydration: a review on its molecular mechanisms. Journal of Cosmetic Dermatology, 6, 75–82. 

Schmid-Wendtner MH, Korting HC. The pH of the skin surface and its impact on the barrier function. Skin Pharmacol Physiol. 2006;19(6):296-302.

Yosipovitch G, Maibach HI. Skin surface pH: a protective acid mantle. Cosmet Toiletries 1996; 111: 101–112. 

Dry Skin Skin Barrier Skin Science

← Older Post Newer Post →



Leave a comment