Special Skin Structures
Causes of cellulite
There are no magic cellulite treatment remedies for selective cellulite removal. It can only be reduced as part of an overall weight reduction program, together with cutting back on calorie intake and increasing exercise, although some fruit acid creams may help to make cellulite temporarily less obvious.
Special skin structures
The skin contains certain important structures with special functions. The lips are specially developed as sense organs. The sweat glands help to regulate body temperature (see Different Skin Types and Their Characteristics). Most of the hairs on a human body have no real function and are a relic of when our ancestors needed warmer 'coats'.
The sebaceous glands
Sebaceous glands are part of the tiny structures - hair follicles - that generate hairs. These glands produce oil, or sebum, which is a mixture of waxes and fats. The glands empty through minute tubes called ducts. Sebaceous glands occur in the skin of every part of the body except on the palms and soles.
Sebum is secreted through the sebaceous duct into the hair follicle. It forms a mixture with the watery secretion of sweat,
which covers the skin and spreads along the hair. The mixture of fat and water forms a natural oil-in-water emulsion (see Moisturizers) which may have a protecting action on the hair. It also kills some fungi that grow on the scalp.
Sebum is slightly acidic (pH between 4.2 and 5.6), which may be why people sometimes refer to the 'acid mantle' of the skin. This is a somewhat misleading expression in that it could wrongly suggest an impenetrable barrier. Skin is in fact permeable in both directions.
In both sexes the sebaceous glands are strongly influenced by male hormones, and are most sensitive to these at puberty, particularly on the face and trunk (the acne areas, see Acne).
Sweat glands
Sweat glands are found in almost every part of the skin, forming tiny coiled tubes embedded in the dermis or subcutaneous fat. There are two types of sweat gland: eccrine glands and apocrine glands.
Eccrine glands produce sweat - a mixture of water and salts. Sweat plays an important part in regulating the temperature of the body by cooling it by evaporation of water from the skin (this is different from the transepidermal water loss through the stratum corneum). It also provides a useful natural method of removing waste products (toxins) from the body. The tiny ducts of the eccrine glands pass through the dermis and epidermis and empty directly on to the skin. They are found everywhere on the skin except on the lips and the glans penis.
Apocrine glands are formed from the same structure as the hair follicle and sebaceous glands. They produce a highly individual sexual scent, the production of which is dependent on the presence of sex hormones. The apocrine glands become very active with the onset of puberty. They are found particularly in the armpit and the genital area. The breasts are modified apocrine sweat glands.
Body odor is produced by micro-organisms ('germs') that grow in particularly moist areas of the skin, such as the armpit. They produce body odor by digesting sebum, but they can only work efficiently if water is present. Antiperspirants can be used to reduce the amount of sweat produced in the armpit, where there are many sweat glands, and stop the germs growing rapidly. The role of antiperspirants for body odor is discussed in Chapter 5, 'Skin care'.
Hairs
Most of the skin is covered in fine hairs called vellus hairs, which are attached to tiny muscles in the dermis. When the air temperature falls, these muscles contract. When they do so the area in the skin to which they are attached is depressed and the skin around the hair 'stands up' - this produces 'goose bumps'. The process is of little or no value in helping us to keep warm.
In babies and children longer, darker and thicker hairs, called terminal hairs, grow on the scalp, eyelids and eyebrows, though nowhere else. In the teens, however, the body starts to produce sex hormones. Both sexes produce some male hormones, and it is these that cause terminal hairs to develop in many other areas such as the beard area, chest, arms and legs. They do not replace the fine vellus hairs - they are still there as well.
Lips
The lips are prominent facial features. They can be divided into three different regions. There is skin on their outer surfaces and a thin smooth lining (mucosa) on the inner surfaces. Between these two tissues lies the vermilion zone (or red zone). It is this zone which people commonly call 'the lips'.
The vermilion zone forms the transitional zone between the mucosa of the mouth and facial skin. It shares some features with the facial skin that surrounds it, but also has some noticeable differences.
The skin of the lips, like skin elsewhere, has a dermis and an epidermis. The epidermis of the lips functions in a similar manner to the epidermis on other parts of the body: it provides a self-renewing barrier, protected from the outer world by a continually exfoliating stratum corneum. The characteristic red color of the lips is unique to humans and comes from the blood vessels in the dermis. The many rete pegs (papillae) are long and narrow, and contain loops full of blood vessels. The closeness of these vessels to the surface, combined with a thin, almost transparent epidermis, gives rise to the red appearance of the lips. In cold weather when the blood vessels close down and the circulation becomes sluggish, the lips look blue.
The ridged appearance of the lips results from a highly folded dermis, which is not found in the skin of other parts of the body.
Chapped lips
There are no hair follicles and sweat glands in the dermis of the lips - this is one of the most marked differences from other parts of the skin. The absence of these features within the lip dermis means that the lubricating effects of sebum are not present in the lips. As a result the lips can easily become dry and chapped. The stratum corneum of the lips is thinner than that of the rest of the skin, worsening this effect. The lips require constant re-hydration keep them healthy and to prevent drying, with the accompanying deterioration in appearance. As everyone has found, licking dry, chapped lips just makes the dryness worse. Only a product like a lip salve can help, because only this can ensure that water molecules accumulate effectively in the stratum corneum. Modern lipsticks can help to protect the lips.
Fingernails
The nails are flattened, elastic structures which are relics of claws. They consist largely of compressed keratin, and are in fact greatly thickened areas of the epidermis. The keratin of the nails is derived from the stratum lucidum (meaning 'the clear layer'), which lies just below the stratum corneum (see The Epidermis). The keratin of the nails can absorb large amounts of water, particularly during a warm soak. This is why nails are softer, and much easier to cut, after a bath.
On average, fingernails grow by half a millimetre or so a week; toenails grow a little more slowly. Growth is said to be quicker in the summer than in winter, and is most rapid in the longer digits.
The white flecks that sometimes appear in the nails are due to minute air bubbles in their structure.
