Page 47 -- FACTORS AFFECTING SKIN FUNCTION

Truly sensitive or atopic skin may:

feel very tight after washing
have a naturally high TEWL rate
react to many external stimuli by becoming red and blotchy
be prone to developing dry flaky patches.

Variation with site on the body

Whatever the type of skin, its state and function will differ from one part of the body to another even in the same individual, and will change from time to time. For example, the face, forearms and hands are most exposed to the elements and may suffer from drying and cracking. The bottom is scarcely ever exposed and the skin there is almost always in near-perfect condition. To really see the differences in skin condition in one person, these are the two areas to examine!
Another characteristic that shows considerable variation is the density of the sebaceous glands. There are many more sebaceous glands per unit area of skin in the upper part of the body (forehead >300 per cm²; chest 60 per cm²; upper back 80 per cm²).

Another example of a variable characteristic is the permeability of the skin: the skin of the palms of the hands is less permeable than that of the forearm, which in turn is less permeable than that of the scalp.
The rate at which the stratum corneum loses corneocytes as squames also depends on the body site. Squames are lost more rapidly from the forearm and back, for example, than from the upper arm and abdomen.

Factors affecting skin function

Environments that dehydrate the skin can considerably affect the skin condition, and hence its functions. Examples include centrally heated and air-conditioned homes and offices.
Out of doors, sun and wind together may produce very severe drying effects, especially if they are experienced over a long period of time.
Water and harsh household detergents and cleaning fluids are the most damaging factors of all, particularly to the hands. People who work as cleaners or apprentice hairdressers expose the skin of their hands to water and chemicals all day long, almost every day. This can result in chronically dry and chapped hands, which may result in a form of irritant dermatitis if left untreated. In turn they may become prone to develop allergies to products with which they come into contact, producing an allergic dermatitis.

Reaction of dry skin to washing.