This is a dead material similar in chemical formula to nails, claws, and compressed to form rhinoceros horn. Some heavy metals are secreted into the hair. Arsenic poisoning can be detected by measuring the arsenic in the hair and it is possible to calculate when and for how long the arsenic was administered. Follicles genetically vary, producing flattened hairs which are curly, or round hairs which are straight. If you flatten a straight hair by running it between two finger nails, it will become curly.
Hairs vary in diameter.
There are thick hairs, as in eye lashes, grading down to fine down-like hairs on different parts of the body. Hair grows on the head or in the beard at about 4 mm a week. Hair usually contains pigmentation making the hair appear black, or brown or red, or blonde. In aging follicles there is little or no pigmentation of the hair and the hair is then white. Oil glands in the skin can secrete a covering to the hair making it appear glossy.