Hyperhidrosis can be divided into two types, depending on whether an obvious cause can be identified. These are known as primary and secondary hyperhidrosis.

Primary hyperhidrosis

Hyperhidrosis that has no obvious cause is known as primary hyperhidrosis.

Although it's not clear why it develops, it's thought to be the result of a problem with part of the nervous system called the sympathetic nervous system, and it's possible your genes may also play a role.

The sympathetic nervous system

The sympathetic nervous system controls most of your body’s functions that do not require conscious thought, such as movement of food through your body and the movement of urine out of your kidneys and into your bladder.

The sympathetic nervous system also acts like a thermostat. If it senses you are getting too hot, it will send a signal from your brain to the millions of sweat glands in your body to produce sweat. The sweat cools on your skin and reduces the temperature of your body.

A specific type of sweat gland, known as the eccrine glands, appears to be involved in hyperhidrosis. There are more eccrine glands on your armpits, hands, feet and face, which may explain why these areas are often affected by hyperhidrosis.

It's thought that in cases of primary hyperhidrosis, the brain sends signals to the eccrine glands, even though there is no need to cool the body.

Genes

Some cases of primary hyperhidrosis appear to run in families, which suggests a genetic mutation may be the cause.

A genetic mutation is where the instructions in your cells become scrambled, which can disrupt the normal workings of the body. Some genetic mutations can be passed down from parents to their children.

Secondary hyperhidrosis

If a cause of hyperhidrosis can be identified, it's known as secondary hyperhidrosis.

Secondary hyperhidrosis can have a number of different triggers, including:

• pregnancy
• the menopause – when a woman’s monthly periods stop
• anxiety
• low blood sugar (hypoglycaemia)
• an overactive thyroid gland (hyperthyroidism)
• obesity
• certain medications – including some antidepressants, propranolol, pilocarpine, and bethanechol
• being drunk or "high" on drugs, or withdrawing from alcohol or drugs if you have become addicted to them
• some infections, such as tuberculosis and HIV
• Parkinson’s disease 
• disorders of the blood cells or bone marrow, such as Hodgkin lymphoma (a cancer of the white blood cells)

Secondary hyperhidrosis often starts more suddenly than primary hyperhidrosis and tends to affect the whole body.