Where Are the Sweat Glands?
Sweat glands, of which everybody has approximately two million, are distributed all over the body on the skin surface. They are not, however, distributed evenly. The palms of our hands and the soles of our feet may have as many as 2,500 sweat glands per square inch, whereas on our backs there may be as few as 500 per square inch.
Each gland breaks the skin surface in the form of a sweat pore. These pores are too small to be visible to the naked eye, except on the palms and the soles, where there are so many that they just become visible.
In some diseases nerve function is lost in certain areas of the body, and these areas also lose the power to sweat. Sweat is a solution of about 99 per cent water with a little sodium chloride (common salt). The body can produce from zero to two thousand grams of this substance every hour and even more in strenuous activities.
Sweat glands are a type of exocrine gland, which are glands that produce and secrete substances onto an epithelial surface by way of a duct. There are two main types of sweat glands that differ in their structure, function, secretory product, mechanism of excretion, anatomic distribution, and distribution across species:
Eccrine sweat glands are distributed almost all over the human body, in varying densities. Its water-based secretion represents a primary form of cooling in humans.
Apocrine sweat glands are mostly limited to the axilla (armpits) and perianal areas in humans. They are not significant for cooling in humans, but are the sole effective sweat glands in hoofed animals, such as the camels, donkeys, horses, and cattle.
Ceruminous glands (which produce ear wax), mammary glands (which produce milk), and ciliary glands in the eyelids are modified apocrine sweat glands.