Hair follicles are tiny tubular chambers of the skin in which hair takes its root and from which it extends up through the epidermal layers. Each follicle aids in supplying its respective hair with blood via a vein, an artery, and a papilla at the bulblike base of the follicle. The follicle itself is based in the subcutaneous layer, beneath the dermis. By excreting oil, follicles act to move dead skin cells to the surface of the skin. For this reason, sebaceous (oil) glands, muscles, and nerves accompany every follicle.
Sebaceous oil-secreting glands are found in all types of skin, all over the body, and usually with a follicle. These glands, which resemble tree branches, are made up of a tube and one or two small sacs that are actually groups of smaller pockets called alveoli. They occur alongside the hair follicle as tiny teardrop appendages. Sebaceous glands excrete oil that is produced when cells in the alveoli die and break apart. Their function is to lubricate hair and to facilitate sweating in the follicle. They do, however, occur in thin, hairless skin, like that of the inside or the mouth, where they aid in the regeneration of cells.
Sweat is a watery substance that is made up of urea (waste product of protein change in the kidneys), fatty acids, and salt. Perspiration is an important function of the skin that cools the body through evaporation and clears the body of waste that can be expelled through its pores. In order to manage such a critical task, the body employs a system of sweat glands that runs throughout the skin. A sweat gland is an elongated tubular structure that originates in the subcutaneous tissue beneath the dermis and extends up to the surface of the epidermis, where it ends at either a pore or a hair follicle. At its secretory base, the gland is coiled and bunched, but its emerging duct straightens as it reaches toward the surface. A sweat gland is one of two types, eccrine or apocrine.
Eccrine sweat glands, of which there are a greater number than apocrine glands in the body, terminate in a pore. Therefore, eccrine glands are predominantly responsible for sweat secretion and cooling the body. They are found everywhere on the body except the rim of the lips and most of the penis. There may be as many as 2,000,000 to 5,000,000 eccrine glands in the body, with the greatest accumulation on the palms.
Apocrine sweat glands open into and feed hair follicles explicitly. They are typically larger than eccrine glands and are more developed in women. They are found in greatest number in the pubic region and in the armpit. When an apocrine gland secretes sweat, some of its cells disintegrate. The product of this disintegration contributes to sweat, which, depending on the amount and type of bacteria it produces, carries an odor that is characteristic of perspiration.
Pigmentation of the skin, eyes, and hair is determined by the presence of melanin in cells of the epidermis called melanocytes. Varying amounts of melanin determine color in both skin type and body part.
In addition to coloring the skin and eyes, melanin actually protects the eyes from excessive harmful UV rays. Melanin absorbs high-energy light, like UV and blue light, more than it does other light in the spectrum. This helps protect the lens as well as the retina, by dispersing light throughout the eye according to its intensity. Overexposure to UV rays causes tanning and burning.