Sweating

Each person has 3–4 million sweat glands At rest in a cool environment, a normal person loses about half a litre of sweat in a day The sweat glands are capable of producing 12 litres of sweat in 24 hours Hippopotamus sweat is red. It contains sunscreen and is also antiseptic (Nature 2004;429:363) We can smell the sweat of a giraffe from a quarter of a mile away. The smell repels ticks (New Scientist 1 February 2003)

Men are sweatier than women, even when you take body size into account. Scientists tested volunteers in a laboratory mock-up of a sweltering car. Men lost 250 g of sweat per hour, which was 70 g more than the women (New Scientist 1 June 2002)

About 3% of people say that they sweat excessively. Of course, we all sweat more when we are hot or anxious but excessive sweating may be partly caused by genes – 1 in 3 sufferers says that others in their family have the same problem. Sweating, accompanying hot flushes, is common in women at the menopause. Occasionally, excessive sweating can signify a medical problem (such as an overactive thyroid gland). Antidepressant drugs can also cause sweating especially of the head and neck (Dermatology in Practice 2005;13(1):24–6).

The uses of sweating Sweating is one of the ways we regulate our body temperature – humans rely on the evaporation of sweat to protect the body against a hot environment (most other animals rely on insulation or panting) Sweat helps to keep our skin moist Sweating of the body and hands when we are anxious may occur for a reason – to help us escape from enemies if they try to grab us Sweat from some areas of the body contains scents (‘pheromones’) that send secret signals to other people According to New Scientist magazine (10 November 2001), sweat contains a natural antibiotic, dermicidin, that helps to destroy bacteria on the skin

There are two sorts of sweat glands.

• Apocrine glands are found mainly in the armpits and near the anus. We each have about 1 million of these glands. They are really scent glands. The sweat that comes from them has a particular smell in each person, and probably includes ‘pheromone’ scents that send messages to other people.
• Eccrine glands are responsible for sweating when we are hot. We each have about 3 million of these glands. Every 1 cm² of the back has about 60 sweat glands. On the palms and soles, there are about 600 glands per cm².

If you sweat excessively, it is not because you have too many sweat glands or that they are abnormally large. It is probably because there is a lot of activity in the tiny nerves that control them.

Worries about sweating

Excessive sweating can be annoying in two ways.

• The sweat may show on your clothes (for example at the armpits) or give you embarrassingly sweaty palms.
• You may be worried about the smell of the sweat. Sweat from most of the sweat glands (i.e. the eccrine glands) is not smelly itself (except the pheromones, which are so subtle that we are not consciously aware of smelling them), but it quickly becomes a breeding ground for bacteria. These bacteria break down sweat to produce fatty acids. It is these fatty acids that have the acrid, penetrating, pungent, ‘stale sweat’ smell. Arm and groin sweat is particularly rich in protein – a favourite of bacteria. Sweat from other parts of the body is saltier and less hospitable to bacteria. This problem can be approached in two ways: sweating itself can be prevented; or the bacteria that cause the smell can be attacked

Doctors are now becoming more sympathetic to people troubled by excessive sweating. They are realizing that excessive sweating can affect your work and social life (British Journal of Dermatology 2002;147:1218–26).

• Sweaty armpits
• Sweaty feet
• Sweaty hands
• Sweating and hot flushes – look at our Blushing & flushing section
• Sweating when you are anxious – look at our Shyness section
• Night sweats
• Pheromones
• Antiperspirants and breast cancer
• Useful contacts