Sweat is essential to human survival and serves as the body’s coolant, protecting it from overheating.
There are two to four million sweat glands distributed all over our bodies. The majority of them are “eccrine” sweat glands, which are found in large numbers on the soles of the feet, the palms, the forehead and cheeks, and in the armpits.
Eccrine glands secrete an odorless, clear fluid that helps the body to control its temperature by promoting heat loss through evaporation. In general, the type of sweat involved in hyperhidrosis is eccrine sweat.
The other type of sweat gland is called an “apocrine” gland. Apocrine glands are found in the armpits and genital region. They produce a thick fluid. When this fluid comes in contact with bacteria on the skin’s surface, it produces a characteristic potent "body odor".
Both the eccrine and apocrine sweat glands are activated by nerves. These nerves respond to a variety of stimuli including:
In people who have excessive sweating, or hyperhidrosis, the sweat glands (eccrine glands in particular) overreact to stimuli and are just generally overactive, producing more sweat than is necessary. It's often said that people with hyperhidrosis have sweat glands that are stuck in the "on" position.
Illustration explanation: The skin is composed of an epidermal layer (E) from which hair follicles (H), sweat glands (G), and sebaceous glands (S) descend into the underlying dermis (D). Attribution: Reprinted from Robbin’s Pathologic Basis of Disease, Edition 6, Cotran, Ramzi S., Chapter 27, Fig 27-1A, Copyright 1999, with permission from Elsevier.