This section is from the book "The Human Body: An Elementary Text-Book Of Anatomy, Physiology, And Hygiene", by H. Newell Martin. Also available from Amazon: The Human Body.
The sebaceous secretion and the solid residue left by evaporating sweat form a solid film over the skin, which tends to choke the mouths of the sweat glands (the so-called " pores " of the skin) and impede their action. Yet these glands, minute though each is, have for their function to separate daily from the body a great amount of water* and some little urea and salines. Hence the importance of personal cleanliness. The whole skin, except that of the scalp, should be washed daily. Women cannot well wash their hair every day, as it takes so long to dry: but there is no reason why a man should not immerse his head when he takes his bath. Except on parts of the skin especially exposed to contamination, soap should only be used occasionally—say once or twice a week; its employment is quite unnecessary for cleanliness, except on exposed parts of the body, if frequent bathing is a habit and the skin be well rubbed afterwards until dry. Soap nearly always contains an excess of alkali, which in itself injures some skins, and, besides, is apt to combine chemically with the sebaceous secretion and carry it too freely away. Persons whose skin is injured by soap, will find in cornmeal a good substitute. No doubt many folk go about in very good health with very little washing; contact with the clothes and other external objects keeps the skin excretions from accumulating to any very great extent. But apart from the duty of personal cleanliness imposed on every one as a member of society in daily intercourse with others, the mere fact that the healthy body can manage to get along under unfavorable conditions is no reason for exposing it to them. A clogged skin throws more work on the lungs and kidneys than their fair share, and the evil consequences may be experienced any day when something else throws another extra strain upon them.
Describe the structure of a sebaceous gland.
Describe the sebaceous secretion. Why is the hair of a healthy person, using no hair-oil. glossy ? Why does water run off the skin?
Enumerate the chief functions of the skin.
How are the mouths of the sweat glands apt to be choked up ? Point out functions of these glands.
How much of the skin should be washed daily ?
* The sweat glands not merely carry off some water from the body, but serve also to regulate its temperature. When water evaporates from the surface of any object it abstracts heat from that object; and when perspiration evaporates it takes more heat from the skin.