We have about 3 million sweat glands distributed over the entire body. Especially in the armpits, on the neck, head, forehead, and on the palms of the hand and the soles of the feet. They are missing on the lips, in the nail bed, eardrums, and to a large extent , in the genital area. On the hands, feet, forehead, and armpits there can be as many as 350 sweat glands per square centimetre.
One differentiates between eccrine and apocrine sweat
Eccrine sweat glands are the most common in the human body and contribute to the majority of the overall amount of sweat produced. They are directly connected to the central temperature regulator in the diencephalons, therefore play a crucial role in regulating body temperature. They do not only excrete water, but also toxins and metabolic end products. Depending on the temperature, sweat glands are able to secrete between 0.5 and 8 litres of liquid per day.
Apocrine glands on the other hand produce a more viscous secretion. They are also referred to as "odour glands". They do not develop until the body reaches puberty. Then they develop mainly in the hair roots, such as in the armpit, around the anus and in the genital area. Odour glands are not main contributors to temperature regulation but are activated during strong emotional conditions, such as anger, pain, fear, or sexual drives. Apocrine sweat is odourless upon release. Only after bacteria or yeast cells decompose the sweat is an unpleasant odour produced. Especially large sweat glands are placed in the armpits and release pungent smelling sweat and produce unpleasant wetness under the arms.
What is sweat composed of?
Sweat consists of up to 99% water and contains not only sodium chloride, but also potassium, magnesium, phosphate, sulphate, urea, volatile low fatty acids, neutral fats, immunoglobulines, cholesterol, and odour substances. Ailments of the sweat glands can be an overproduction(hyperhidrosis), under production(hypohidrosis), or complete loss of production(anhidrosis).