What Soap Does to Your Skin

What Soap Does to Your Skin

By Heather Brannon, MD, About.com

http://dermatology.about.com/b/2008/03/23/what-soap-does-to-your-skin.htm

Updated: March 02, 2008

About.com Health's Disease and Condition content is reviewed by the Medical Review Board

Cleansers are designed to remove dirt, sweat, sebum, and oils from the skin through the action of surfactants. Surfactants work by surrounding dirt particles and oils, dissolving them in water, and removing them as water runs over the skin. In addition surfactants aid in the normal exfoliation process of the skin. However, surfactants can also have the following harmful effects on the stratum corneum, or outer layer of the epidermis:

After-wash tightness (AWT)

Dryness

Damage to the barrier function of the skin

Redness

Irritation

Itching

Cleanser Interaction with Stratum Corneum


It is helpful to understand how cleansers interact with various components of the stratum corneum.

Cleanser Interaction with Stratum Corneum Proteins


Corneocytes are protein complexes made of threads of keratin in an organized matrix. Cleanser surfactants bind to these proteins allowing them to become over-hydrated and swell. This swelling can make it easier for the cleanser ingredients to penetrate into the lower layers of the skin where they can interact with the nerve endings and immune system, possibly causing itching and irritation. When the water evaporates it leaves the corneocytes dryer than before. Finally cleansers can cause a reduction in the level of natural moisturizing factor (NMF) in the stratum corneum.

Cleanser Interaction with Stratum Corneum Lipids


The exact effects of cleansers on lipids in the stratum corneum are still not completely understood. It appears that certain surfactants get between the lipid bilayer causing increased permeability and even disruption of the bilayer. Surfactants can also cause damage to the lipid structures themselves causing a reduction in the amount of lipids in the skin.

Cleanser pH Effect on Stratum Corneum


Surfactants in cleansers are broadly divided into soap-based surfactants and synthetic detergent-based surfactants (syndets). Soap-based cleansers are more alkaline (pH 10) than syndets (pH 7 or less). It appears that the higher pH of soap bars is a major factor in the increased irritation seen with these cleansers, however the exact mechanism is still unknown.

Key Words: Stratum Corneum, surfactants, NMF