In our body there are more than four million sweat glands. There are two types:eccrine and apocrine. The eccrine glands are responsible for the physiological function of regulating the body temperature and eliminating toxins. These glands can produce excessive amounts of sweat under conditions of fear, anger, sorrow, physical pain, embarrassment, stress, and heavy physical exercise. The apocrine sweat glands, on the other hand, react exclusively to stimuli from the nervous system (involuntary) and hormones. Sweat is odourless until it makes contact with skin bacteria, and breaks down to form new substances which often have an unpleasant smell.

Contrary to other mammals, man has sweat glands spread around the whole body, but they are not evenly distributed. They are mainly concentrated in hands, feet, forehead and underarms. We have more than 25,000 underarm sweat glands, both of the apocrine and the eccrine types.

Under-arm perspiration becomes excessive when the eccrine glands are exessively stimulated by fear, heat, sadness, anger, stress, emotional reasons and /or heavy physical exercise. It is also, although rarely, caused by excessive stimulation of the apocrine glands due to hormonal disfunction or disorders of the nervous system.
Excessive perspiration is in medical terms called hyperhidrosis, which is an ailment suffered by 5% of the adult population.