Moisturizing mechanism, MVEs; ph-balanced cleansers

October 21, 2005

This seems like a very simple question, but in actuality is quite complex. Just walk up and down the drug store aisle and look at all of the moisturizers. Each manufacturer claims to have found the perfect method for skin moisturization, but in actuality, all companies are still searching for the complete answer. How do I know this? Simply because each year new moisturizers enter the market and older versions are withdrawn.

Q. How is the skin moisturized?

What is known is that there are certain methods by which the skin cannot be moisturized. These include spraying water on the skin surface through misting or compresses. Water applied on top of the skin causes maceration, actually destroying the barrier. Furthermore, drinking eight glasses of water a day does not remoisturize dry skin. While adequate dietary water content is very important, excess water intake does not influence skin water content. Hot, humid environments, such as steam baths and wet saunas, do not increase skin moisturization. Neither does covering the skin with plastic wrap, mudpacks or other dressings. Skin coverings will work while the wrap is in place, but transepidermal water loss will return to the pretreatment level if no barrier repair has occurred.

What is the normal water content of the skin? This is somewhat controversial depending on how the water is measured. It is probably somewhere between 20 percent to 30 percent, although some authors report levels exceeding 30 percent. Too little water creates cracks and fissures, through which water is lost to a lower humidity environment, and too much water causes white, macerated skin. Basically, equilibrium between the external climate and internal environment of the body occurs at about 70 percent humidity. So, if you take someone with impaired barrier function and you put them in a room where the humidity is 70 percent, transepidermal water loss will be zero. But, think about an ambient humidity of 70 percent. A 70 percent humidity room is very damp, usually with water dripping from the ceiling. It is for this reason, humans need a skin barrier, because we do not live in climactic conditions of 70 percent ambient humidity.

So how can the water content of the skin then be maintained given all these requirements?

We live in a world of controlled environments with an ambient humidity somewhere around 27 percent to 30 percent. This means the role of a moisturizer is three-fold. It is a man-made barrier to evaporation. It is an environment created for optimal healing. Lastly, it maintains the barrier so damage does not occur. If a moisturizer accomplishes these three goals, the water content of the skin can be maintained.

Thus, the skin is moisturized by preventing it from drying out through stopping transepidermal water loss. The major function of a moisturizer is to stop water loss by putting a semipermeable film over the skin surface, which enhances barrier repair. What the constituents are of the semipermeable film and how it smells and looks differentiates all of the numerous moisturizers on the market today!

Q. What is pH-balanced soap? Does it offer any advantages to my patients?

A. Believe it or not, this is a source of tremendous controversy within the cleanser manufacturing industry.

There are those who believe that the pH of the cleanser is most important to skin mildness, while others believe it is the composition of the surfactants in the cleanser. A pH-balanced cleanser is formulated with pH adjusters to make the bar neutral with a pH around five-and-a-half to seven. However, it is important to understand that soap is not a generic term for a bar cleanser.

Soap implies a very specific formulation created by chemically reacting a fat and an alkali to create a fatty acid salt with detergent properties. Soap has an alkaline pH between nine and 10. Soap efficiently removes both sebum and intercellular lipids. Soap cannot distinguish between the lipid that holds the skin cells together and the sebum on the skin surface.

This has led to development of a new cleanser known as a syndet that accounts for almost all the products in a dermatologist's sample closet. Syndet is a contraction for synthetic detergent. The most popular syndet bars have a pH between five-and-a-half and seven. This more neutral pH removes fewer intercellular lipids.