What Causes Underarm Sweating?

M.C. Huguelet

Those who have suffered from embarrassing odor and stains in the armpit region may wonder why their underarms must produce sweat. Like all sweating, underarm sweating is often a function of the body’s temperature regulation system. It may also occur in response to emotional situations or due to a hereditary predisposition for perspiration. Unfortunately, the anatomy and positioning of the underarms makes them hospitable to sweat-eating bacteria, which can translate to body odor. With a few simple measures, however, it is usually possible to prevent underarm sweating from becoming a significant problem.

Underarm sweating is a function of the body's temperature regulation system.
Underarm sweating is a function of the body's temperature regulation system.

Every person’s underarms have two distinct types of sweat glands. The first type, known as an eccrine gland, is found on most of the skin’s surface. Another type, known as an apocrine gland, is found in areas where the hair grows densely. Specifically, apocrine glands are found on the groin, the top of the head, and the underarms.

Bathing daily and washing one's armpits can discourage underarm bacteria.
Bathing daily and washing one's armpits can discourage underarm bacteria.

Eccrine glands, which begin below the skin and terminate on the skin’s surface, are a vital part of the body’s temperature regulation system. When the body begins to grow warm, eccrine glands in the underarm area and elsewhere release a water- and salt-based sweat onto the skin’s surface. As this fluid evaporates, the body begins to cool down.

A diagram of the human skin, including sweat glands.
A diagram of the human skin, including sweat glands.

Underarm sweating that is driven by the apocrine glands, on the other hand, is not so closely linked to temperature regulation. These glands, which begin below the skin’s surface and terminate in the hair follicles, carry sweat that is rich in fats and protein. When triggered by an emotional situation, a hereditary predisposition for perspiration, or a surge of hormones, the apocrine glands contract, sending this fatty sweat into the hair follicles. The sweat then travels up the hair follicle and is released onto the skin of the underarms.

In general, it is apocrine gland-driven underarm sweating which is responsible for underarm odor. This is because the bacteria which occur naturally on the skin’s surface feed on the fats and proteins contained in apocrine sweat. After feeding, these bacteria release waste which produces a foul odor when it mixes with perspiration. Due to their high concentration of apocrine glands combined with the fact that they are usually dark and moist, the underarms provide a haven for these bacteria and the odor they cause.

Luckily, with a few simple steps, it is usually possible to prevent underarm sweating from becoming a major problem. Using a combination antiperspirant and deodorant can temporarily block underarm sweat glands while reducing the number of bacteria in the area. Proper hygiene, including bathing daily and washing one’s clothes regularly, can also discourage underarm bacteria. Finally, wearing loose-fitting clothes made from natural fibers such as cotton can reduce sweating by allowing the skin to breathe.

A stick of deodorant.
A stick of deodorant.

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