Causes of Perspiration

As a part of the body's cooling system, perspiration protects the body from heat induced illness and harm. The American Academy of Dermatology notes that special variations of sweat glands in the ears produce ear wax, a type of perspiration that protects the ear canal. Other specialized sweat glands produce breast milk. In animals, and possibly in humans, sweat glands produce pheromones to attract mates.

Thermoregulation

The human body uses perspiration as a part of its thermoregulatory response to over-heating. The body has two types of sweat gland---eccrine sweat glands and apocrine sweat glands---as well as a hybrid gland, called the apoeccrine gland. Eccrine glands play the biggest role in thermoregulation.
Eccrine sweat glands are functional at birth and make up the greatest number of the approximately 3 to 4 million sweat glands on an adult body. While these glands are dispersed over the entire body, they are most prevalent on the palms, soles and forehead.
When exposed to ambient temperatures greater than an individual's resting temperature--98.2 degrees Fahrenheit, according to Harvard Health Publications--temperature receptors on the skin and thermo-sensitive neurons in the brain alert the body to instigate a cooling process to draw heat away from the body's core and to send it to the skin. The sweating process lowers the body's core temperature while evaporation of sweat, in a process called "evaporative cooling" according to the Department of Physiology of Indiana University's Medical School, lowers surface temperatures.
Eccrine sweat makes up the wet portion of underarm sweat, according to the American Academy of Dermatology. The apoeccrine sweat glands develop at puberty and are primarily located in the axillae, or underarms. These glands open directly to the skin and produce ten times as much sweat as eccrine glands. Exercise and fever also trigger a thermoregulatory response that involves perspiration.

Scent Production

The American Academy of Dermatology points out that apocrine sweat glands only become functional at puberty. These glands produce a more viscous fluid than do eccrine glands and produce smaller amounts of fluid. Located in the axillae and anogenital regions of the body and, to a lesser degree, around the nipples, these glands are thought to represent scent glands. In the book, "Dermatology, Volume 2," subject authors Martin Schaller and Gerd Plewig, point out that in animals, the perspiration put out by apocrine sweat glands functions as pheromones (chemicals that instigate a response, such as sexual attraction). They hypothesize that the function may be similar in humans. When their odorless fluid reaches the surface of the skin, bacteria that normally live on the skin decompose the fluid and produce the odor usually associated with sweat.

Emotional Responses

Apocrine sweat glands continuously put out minute amounts of perspiration. These glands respond primarily to emotional triggers, such as fear and embarrassment. Dermaxine notes that during periods of stress and high emotion, the apocrine glands excrete more perspiration than normal.

Diseases and Medications

A number of diseases and medications can influence perspiration outputs. The International Hyperhidrosis Society offers lists of common medications and conditions that are known to increase sweating. Generic drugs include Acyclovir, Buproprion and Citalopram. Medical conditions that promote perspiration include menopause, obesity, Parkinson's disease and rheumatoid arthritis.