Dry skin is also referred to as Xerosis

(xeros is Greek for “dry”) Alternative Names: Asteatotic eczema; Eczema craquele

Skin care for dry skin requires moisture in order to maintain the skin’s smoothness and suppleness and especially during winter, this can be particularly difficult. In addition, adequate moisture in the skin is important in maintaining the pH balance of your skin.

Normally, the chemical composition of the stratum corneum (the outermost layer of the epidermis) is quite stable, except for the water content, which varies between 10% and 60% in different environments and diminishes near the surface of the skin.

Also, the number of corneocyte layers in nonpalmoplantar skin (usually 15–30) is normally rather constant, reflecting a balance between basal cell proliferation and keratinocyte shedding from the surface. Corneocyte cohesion is jointly accomplished by desmosomes and intercellular lipids, structures that are gradually modified as cells move toward the surface.

This process appears to be partially controlled by pH-dependent enzymes expressed in the intercorneocyte space.

It is common knowledge that the pH on the surface of nonoccluded human skin is around 5, as against 7.4 in viable epidermis. This implies that a change of more than 2 pH units occurs over a distance of only about 10 m in the epidermis (normal thickness of human stratum corneum).

pH and the Acid Mantle

The term pH stands for the “potential of Hydrogen”. It is a measure of the Hydrogen ion concentration of a substance. The Hydrogen ion concentration is more commonly referred to as the acidity or alkalinity level. The more acidity in the substance, the lower the pH, the less acidity, the higher the pH. There are differing values of pH in the body depending on what function is being performed. For example, the pH of the stomach is very acidic, around 1, because stomach acids help break down the foods we eat. Our saliva and blood, on the other hand, are much closer to neutral. Neutral substances, like water, have a pH of 7. A pH above 7 is considered alkaline (less acidic), and a pH below 7 is considered acidic.

The pH system works in 10-fold multiples and each pH unit represents a 10-fold difference in alkalinity. For example, a soap with a pH of 10.5 has 10-times the alkalinity of a soap of pH 9.5. “Mild” soaps are often alkaline (pH 9.5-11), and remove the natural acid protection as well as extracting protective lipids (fats) from the skin. Irritated and eczematous skins tend to have a more alkaline pH, and washing with soap can increase this alkaline state and make the skin even more vulnerable to irritation and infection.

The acid mantle is a thin oily film that sits on top of the outmost layer of our skin. For most people, the pH of the acid mantle is about 4.5 to 5.5.

Three classes of molecules are the most likely source of protons in normal stratum corneum: (i) certain amino acids and filaggrin-related breakdown products, e.g., urocanic acid and pyrrolidone carboxylic acid (Warner et al. 1995), also known as the “natural moisturizing factor” (Scott et al. 1982; Rawlings et al. 1994); (ii) alfa-hydroxy acids, such as lactic acid and butyric acid, which are naturally present in sweat and possibly other components of the skin (Rothman 1954); and (iii) acidic lipids, e.g., cholesterol sulfate and free fatty acids, which are either synthesized de novo in the epidermis or deposited onto the skin surface in areas with a high sebaceous activity (Elias 1983).

On the basis of known facts and educated assumptions about the concentrations of these three classes of molecules in human stratum corneum, it is possible to correlate their appearance to the pH profiles (or proton gradients) in normal and ichthyotic skin. Hence “the acid mantle of the skin” is a combined effect of acidic excretion products from sweat and sebum, and hydrolytic products of filaggrin originating in the granular layer and further concentrated in the upper stratum corneum partially as the result of desiccation.

Ichthyosis is a collective name for diseases characterized by generalized xerosis, hyperkeratosis, and scaliness of the skin. The two most common forms of the diseases, autosomal dominant ichthyosis vulgaris (IV) and x-linked recessive ichthyosis (XRI), usually occur at frequencies of 1/250 and 1/3000, respectively.

The abnormal gradients in autosomal dominant ichthyotic skin are explained by a depletion of urocanic acid and pyrrolidone carboxylic acid due to filaggrin deficiency (a genetic disorder) presumably delays the accumulation of protons and moves the pH gradient outwards in ichthyosis vulgaris skin. Conversely, the downward transpositioning of the pH gradient in x-linked recessive ichthyosis is probably the combined effect of cholesterol sulfate accumulation and xerosis in the upper strateum corneum.

The “acid mantle” of normal skin, which penetrates deep into the stratum corneum, is the combined result of cornification-associated organic acids and back-diffusion of acid material from the surface. Because corneocyte desquamation involves many pH-dependent enzymes, abnormalities in the transcorneal pH gradient play an important role in the pathogenesis of ichthyosis.

Why is our skin naturally acidic at the surface?

Our slightly acidic skin helps to fight off harmful bacteria. Many of the contaminants that might enter our skin, such as chemicals from the atmosphere and harmful bacteria, are alkaline in nature (i.e., they have a pH of higher than 7). Our skin’s natural acidity neutralizes these chemicals and bacteria, much the same way the milk of magnesia neutralizes stomach acid when we have heartburn.

Neutralizing these harmful contaminants is part of the body’s defense system. Maintaining the skin pH at the proper level is vital to protecting ourselves from harmful bacteria which can lead to acne, infection, or irritation.

Most of us use soap and water to clean our faces without realizing that this may not be beneficial to us. Soapy water is highly alkaline (with a pH of 12) while our skin is naturally acidic (with a pH of approximately 5). Soapy water is commonly used to clean our faces because it removes the natural oils from the skin. While this leaves our skin with that “clean feeling,” soap is actually neutralizing our skins acid pH thereby stripping away our natural defense systems. Particularly for those of us that wash our faces 2, 3, or 4 times a day because of a problem condition like acne, stripping away the acid mantle can actually worsen our condition. Similarly it is important to know the pH of any cleansers, moisturizers, makeup and other products we use so that we don’t remove the protective oils and acid mantle from our skin.

If you do need to use soap, make sure it is of a neutral to slightly acid pH, as your skin is slightly acid and an alkaline soap will disturb the pH balance. In addition, make sure there are no harsh chemicals contained in your soap, as this will remove the ‘Acid Mantel’ and cause your skin to dry out.

Caring for dry skin requires the use of a correct skin care regime and the application of natural skin care products to counteract the drying of your skin. By following the suggestions below, you will reduce the dryness of your skin and promote a healthy vibrant complexion, all over.