Normal water content of the stratum corneum (SC): 30%

When the moisture content decreases, the skin breaks down filaggrin into free amino acids. This step helps restore moisture to the skin but decreases its effectiveness as a barrier.

When the SC moisture content is low, cells are shed more slowly, leading to dry, rough, scaly skin.

Intercellular lipids in the SC prevent water and natural moisturizing factors from leaching out.

Natural moisturizing factors (NMFs) are free amino acids and other physiological chemicals that attract and hold water to keep the skin moist and pliable.

Cholesterol is a vital component of the SC. It is primarily synthesized from acetate in cells; very little dietary cholestorol is found in the SC.

While humectants are designed to add moisture, this moisture is pulled from deeper layers of skin, not usually from moisture in the air or from water in a topical moisturizer..

Frequent Causes of Dry Skin:

Age. After age 40, there is a sharp decrease in the levels of intercellular lipids.

Low Ambient Humidity. More filaggrin is broken down in dry weather, leading to a loss of barrier strength.

Solvents, detergents, soap/water, alchohol-based hand rubs. Chemical and mechanical action removes intercellular lipids and NMFs. Solvents (e.g., alcohol) also denature proteins in the SC, causing a loss of resiliency.

Repeated water exposure. Water-soluble NMFs and some lipids are lost when skin is exposed to water for a long period. Water also changes the skin environment and disrupts the normal skin flora, increasing chances of infection.

Sun damage. Studies have shown that skin hydration decreases significantly 24 hours after sun exposure.

Chronic illness. Studies indicate that the skin, particularly on the hands and feet, of diabetics is much drier than normal skin. Medications for a variety of illnesses may also lead to temporary or chronic dry skin.

Why does it matter if my skin is dry?

The SC forms a barrier between the deeper, more sensitive layers of skin and the harsh environment. When the SC becomes dry and flaky, it cannot protect you as well as it should from germs, allergens, and irritants. Dry skin frequently itches, and scratching leads to irritation while allowing easier passage for germs and other organisms.