Functions of the Skin. The skin and the various glands connected with it form a complex organism with functions of great importance in the work which the body has to do. These functions may be classified as protective, sensory, respiratory, heat-regulating, and secretory. The skin protects the body from injuries from without and also acts as a guard against a too rapid loss of the liquids and heat from within. Thus the skin protects the muscles, nerves, and blood vessels from such dangers as might be caused by blows or pressure, as well as from the injurious effects of high and low temperatures. As the skin forms a sensory covering to the body, it conveys the sensations of pressure, temperature, and pain so that the body may adapt itself to changes in its environment. The skin aids the lungs in their work of respiration and, like the lungs, throws off water and carbon dioxide, and absorbs oxygen. The respiratory work done by the skin, however, is only a minute fraction of that which the lungs do.

The heat-regulating function of the skin is its most important work. In this the skin is aided by the two million or more sweat-glands which are distributed over almost the entire surface of the body. The skin and the sweat-glands together serve to keep the blood at an even temperature, either by giving off heat or in preventing this process in case the outside air is too cool. The body temperature is, as a rule, higher than that of the outside air so that heat is generally being given off by the skin. We are perspiring constantly, but usually to such a slight extent that we hardly notice the fact. The amount of heat which is thrown off at any time is proportional to the amount of the body surface. Through exercise the amount of heat is increased and sweat is produced and given off. Thus sweating is merely another method of getting rid of heat. The body becomes too hot, either through an increased burning of food and tissue within, or because of increased heat outside. In either case sweat is produced and collects on the skin. It is estimated that fifteen per cent of the total heat of the body is given off through the skin, and ten per cent by the lungs.

The condition of the air influences the amount of work which the sweat-glands do and the amount of perspiration thrown off. If the air is full of moisture, the perspiration does not evaporate and the heat becomes excessive. If the air is dry, the perspiration evaporates rapidly and the body is cooled. Over one liter, or one quart, of perspiration is thrown off by the skin every twenty-four hours. While the skin and its glands keep the heat of the body well regulated, the changes of climate are so great that animals are provided with hair for further protection against the changes in temperature. On the other hand, man uses clothes for this purpose. Perspiration may be caused by other things than by heat and exercise. The nervous system is an important factor, as the "cold sweat" of fright shows.

The sweat and sebaceous glands are the secretory glands of the skin, which secrete the water and fats that the skin needs very badly to keep it lubricated and in a working condition. This fat or grease is furnished by the sebaceous glands. If a person has greasy hair, it means that the sebaceous glands of the hair have an over-secretion of grease. These glands form an additional layer of fat on the surface of the skin, and the oily substance from them protects the skin from losing a large quantity of heat.

The proper hygiene of the skin depends upon a wise selection of food, a proper amount of exercise, careful attention to bathing, and suitable clothing. The functions of the skin may be impeded by neglect of any of these essentials, but absolute cleanliness is, perhaps, the most imperative of all.

Clothing. The matter of clothes is not one of vital moment in the care of the health. Clothes were not originally intended for the purpose of keeping warm, but rather to increase the sexual attractiveness of the individual. As we have become civilized, however, we have lost sight of the original idea of clothes, and they are now worn as a matter of decency and to keep the body warm.

As an important function of air is to act as a cooling apparatus, clothes should never interfere with this. Clothes should be sufficiently loose to allow a reasonable circulation of air around the body. This means that the air should have free access to the skin, and that all outer clothes should be loose and porous. Tight clothes interfere with the normal functions of the parts of the body which they cover. We are coming to realize more and more the benefits of wearing as few clothes as possible, and only the minimum amount that will secure warmth should be worn.

In selecting clothing to be worn for the preservation of heat, it should be remembered that certain colors attract, while others reflect heat. Black absorbs heat to the greatest extent, and white the least. The more nearly white the clothes the better.

Wool makes the most desirable articles of clothing, for it is not only warm but it also absorbs moisture,—an important point. But as woolen cloth does not give off moisture rapidly, it is undesirable for underclothing, as the retained perspiration works to the disadvantage of the skin. Cotton cloth is preferable during hot weather, as it does not keep the body warm, and, being thin, allows a proper circulation of air. All animal coverings are warm, due to the fact that in addition to the highly impervious skin layer there is also considerable air in the mesh of the coat. The same result may be obtained with layers of paper, for with the air spaces between the layers, there is little conduction of heat.

It is perhaps unnecessary to add that clothing should be kept clean and well aired. Damp clothing aids the growth of micro-organisms and, helped by the heat of the body, favors the development of parasitic skin diseases.

Bathing. The presence of perspiration and grease from the glands makes it imperative that the skin be cleaned carefully in order that it may freely perform its functions. The relation of baths to health is a curious one, for we cannot say that baths are absolutely essential to health. To a certain extent it is true that bathing is largely for cosmetic purposes and only indirectly for purposes of hygiene. The hands, the face, and finger nails, however, must be washed with care, especially before meals and before food is prepared. This rids the surface of the skin of any kind of infection which may be present. Neglect of such precautions is responsible for the spread of various bacterial and parasitic diseases. Soap dissolves the products of the glands, which may remain on the skin and which may prevent their doing their proper work.

A cold bath has a stimulating effect on the body. It sends the blood to the skin, increases the heart action, warms the body, and gives a good circulation of blood throughout the body. This means that the cold bath has stimulated the metabolism of the body in every way. But the value of the cold bath should not be over-emphasized—it is simply a method of stimulation. If the cold bath is too prolonged or too cold, the body is chilled and the heat-regulating mechanism is disturbed with possible bad effects. Some persons are easily affected by cold baths,—their systems do not react, so that cold baths are harmful to them.

A warm bath, on the contrary, acts as a sedative. It is slightly warmer than the body and so relieves the work of the body for a time. The most important thing about all baths is the securing of personal cleanliness, which is best obtained by the use of hot water and soap. It should be remembered, however, that a prolonged hot bath which disturbes the heat-regulating mechanism is harmful.

Under ordinary conditions the skin remains smooth and requires little real attention. The natural moisture and oil provided by the glands keep it lubricated and soft. Still the skin may be disturbed in a number of ways. One is by mechanical conditions such as heat and cold. Burns illustrate the effect of too great heat, while the effects of cold run all the way from chapped hands to the freezing of different parts of the body.

The Skin and Diet. There is considerable controversy over the effect of diet upon the skin, but there is no question that it has a certain influence. When people take an insufficient amount of water, the skin becomes too dry. Then in the case of an abnormal skin diet plays a considerable part. The classical example is the satiny skin, the pimples, and the red nose as the result of alcoholic excess. Such effects, however, should be regarded as the result of the use of a poison. Drugs, which should always be regarded as poisons, cause skin trouble. Among such drugs are potassium iodide and potassium bromide. Even quinine may cause a skin rash. Furthermore, it is known that constipation causes a muddy skin or acne.

We may also take in certain poisons in our food, which cause skin trouble. In the case of anaphylaxis, where certain individuals are susceptible to definite kinds of food, one of the evidences of the poison is the rash known as the hives. Of course the avoidance of that kind of food is the treatment in such a case.

Disturbances of the Skin. Pimples, or acne, is caused by a disorder of the sebaceous glands. Usually there is first an overactivity of the glands, and, subsequently, some infection of them. The evidence of this disease is the familiar greasy, dull brownish skin, with pimples, blackheads, and pustules. It is especially striking that acne is prevalent just at the time or just after the time of reaching puberty. This is due to the increased activity and growth of the hair on the body and face at that period of growth. With the development of hair follicles comes the development of the sebaceous glands, but in young women the sebaceous glands of the face may become overactive without an increase of hair. This abnormal activity or restlessness of the skin is greatly increased by poor habits of hygiene. Probably much of this trouble comes through a badly regulated diet. At any rate people are aware that so long as they keep in good condition and take good care of themselves there is little likelihood of acne. In other words, ordinary hygiene, a reasonable diet, regular meals, regular hours, and the scrupulous care of the bowels, is the best prevention and cure of acne. Local applications under medical supervision are, of course, of great value.

Eczema causes approximately one-fifth of all the skin troubles. This condition of the skin is also known as salt rheum, and is characterized by a variety of appearances, perhaps most commonly by red, weeping surfaces, itchy, red pimples, and rough, thickened areas. We are ignorant of the exact cause of the disease and, consequently, there is no particular prevention. At present eczema is ascribed by some authorities to an inability to digest certain kinds of foods, which thus produce substances that come to the skin and irritate from within. It is probable that in some cases eczema has an association with the external irritation of the skin, and so care should be taken to protect the skin from scratching and other irritations. The treatment of eczema varies in different cases and should be placed under the care of a physician at the first appearance of the disease. Early treatment is imperative, for, in this stage, the disease yields readily, but, if it becomes deep-seated, it may be very difficult to eradicate.

Associated with the sebaceous activity in acne, is another condition known as dandruff, and allied with that the condition known as baldness. Heredity plays a large part in producing baldness, and in certain families baldness occurs almost inevitably at an early age despite any and all treatment. This is probably due to the fact that the vigor of the hair dies out. Baldness is also caused by dandruff and a poor condition of the scalp. It is hardly necessary to say that the hair and head should be kept clean, but continual shampooing does more harm than good except in a few isolated cases. It is a safe rule never to put on the scalp anything but the simplest things, and shampooing at intervals of two or three weeks is usually sufficient to keep the hair in good condition.

In certain families there is a tendency for the hair to turn gray or white at an early age. There is practically nothing that can be done to prevent this. Hair dyes should never be used. In case lead hair dyes are used there is an excellent chance of contracting lead poisoning, and, in any event, nearly all hair dyes injure the hair and irritate the scalp.

Other inflammatory conditions of the skin—the various forms of dermatitis—are well known to everyone. The inflammation caused by poison ivy is a familiar form of dermatitis. Most people are susceptible to this poison, but certain individuals are more likely to be affected seriously than others. One attack of ivy poisoning seems to add to the susceptibility. The fuzz of brown-tail moths also causes an uncomfortable form of itching dermatitis. Furs which have been kept in preservatives also cause irritation, but this can be prevented by keeping the furs clean.

A number of the disturbances of the skin are contagious. A common infection is the wart, although we do not know how the infection is carried nor what the cause may be. There have even been epidemics of warts in various schools. Numerous superstitions have arisen concerning warts—the lore of every boy and girl—due to the fact that warts disappear suddenly and with no apparent reason. There is no way to prevent warts except the ordinary prevention of any infection,—cleanliness. It is not always wise to have warts cut off or burned away with acid, for Nature will usually take care of them and then no unsightly scar remains.

"Red flap" is an infection of the skin that is especially common on the athletic field. This starts between the legs or under the arm-pits as a seeming irritation. This is really an infection by a certain mold. Once started the contagion, which is easily carried by such articles as towels, may spread to all members of the athletic team. As it is contagious, it should be treated like any other contagion, that is by segregation of the individual sufferer. The prevention is by scrupulous cleanliness of body and clothes, and cleanly habits in the use of towels.

Boils, another form of skin infection, are caused by a definite bacterium, the staphylococcus aureus. This is a pus-forming bacterium which occurs widely and often lurks on the surface of the skin. Once the bacterium gets into the skin it may be difficult to dislodge. Boils occur commonly on the back of the neck and there is a definite reason for this. The rubbing of the collar starts the trouble; then the germ gets into the skin, and a pimple is formed. If this pimple is irritated, the germs are spread still further, and a boil is formed. If the sufferer is particuarly unlucky, a carbuncle may result. The spreading of boils is extremely easy, but it is, nevertheless, due to gross carelessness. There is, of course, a degree of individual susceptibility. The avoidance of boils is simply a matter of strict personal hygiene and cleanliness, as well as the recognition of the fact that the germs may be spread all over the body and transmitted to others. The most frequent method of transmission of the germs is by the hands, and the conclusion here is the obvious one of scrupulous personal hygiene. Boils are a typical example of a skin infection which comes from a germ and finds an opening through an irritation of the skin.

The "seven years itch" or scabies is another example of skin infection for which personal cleanliness is the only preventive. This condition causes much annoyance if it is not treated both immediately and drastically. It is popularly supposed that the "seven years itch" is a condition which does not occur in the higher conditions of society, but such is not the case. It is caused by a small animal parasite that burrows in the skin. That this itch spreads easily from person to person is shown by the tremendous prevalence of scabies in the armies of France during 1914 when bathing facilities were deficient.

Other animal parasites, such as lice, which cause skin lesions, and other molds, such as ringworm, can be avoided by ordinary habits of cleanliness. Such personal cleanliness should include not only contact with other human beings, but also with the lower animals, for ringworm is often spread by the domestic animals. The treatment of these conditions is a matter for medical advice in each instance.

Roger I. Lee

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