Many people experience sweaty feet occasionally. However, for some people excessive foot sweating is a persisting problem which can be both difficult to manage and embarrassing.
How is sweat produced?
Sweat is produced in sweat glands, which are distributed all over the body. With the exception of specialised sweat glands in the armpit and groin, most sweat glands are of a type called eccrine glands. They are set deep in the skin, and are served by nerves and arteries.
The number of working sweat glands varies between parts of the body - and also between different people. In a pair of feet there are normally about 250,000 sweat glands which typically produce about half a pint of perspiration a day. Sweat glands are more concentrated on the feet than in any other part of the body.
When sweating activity is low only a small proportion of the glands will be working - as sweating increases, more glands are 'recruited'. The differences between people in terms of how much they sweat are in part due to how quickly and readily their glands are called into action.
Sweat is mostly water. However, it does contain some salts, including sodium chloride - which is why it has a salty taste.
How much do feet normally sweat?
The total amount of sweat we produce depends on the number of working sweat glands and their activity. This activity is regulated by nerves and hormones and affected by gender (men sweat more than women). When all the sweat glands are working at maximum capacity, the rate of perspiration for a human being may exceed three litres an hour.
Are there other kinds of sweat glands in the feet?
Apocrine glands are found in the armpit and groin. These differ from eccrine glands in that their sweat contains hormones, proteins and sebum and is oily and cloudy. However, they are not present in the feet.
Why do my feet sweat?
Sweating has three primary functions:
- Heat regulation - sweating cools the body by wetting the surface of the skin.
- Excretion - another way for the body to get rid of water and salts.
- Skin protection - sweat is slightly acidic and this helps protect the skin from germs (bacteria). Sweat also helps keep the skin supple.
Sweating on the soles has a fourth possible function of increasing friction on bare feet. This is thought to have helped our ancestors to increase the grip of feet on the ground when running from predators or any other threat.
What makes you sweat more?
Excessive sweating most often occurs on palms, soles, face, scalp and armpits. Anyone can experience it. However, it's more common in teenagers and pregnant women because hormonal changes make them sweat more. The common causes of increased foot sweating are:
- Heat - both external heat and also high body temperature (fever). Sweating is an important way of reducing body temperature when it threatens to rise. In heatstroke, when the eccrine glands become exhausted and unable to sweat, the body temperature rises rapidly and can lead to death.
- Strenuous activity and a warm environment will contribute to sweaty feet.
- Emotion. Excess foot sweating is brought on by anxiety or emotional stress.
- Eating (this usually affects only the head and neck).
- Damage to the sympathetic nerves. These are a special set of nerves involved in stress responses. This can be due to trauma or to medical conditions such as diabetes.
- Footwear. Some shoes and socks can increase the amount of sweat you produce and may prevent it from evaporating.
- Being on your feet all day. You're more likely to have sweaty feet if you're standing all day.
- Obesity. Being overweight is associated with increased sweating.
- Generalised excessive sweating (hyperhidrosis). Sweaty feet are seen in people with generalised hyperhidrosis (see below). Sometimes hyperhidrosis affects the feet only.
- Some prescribed medications - particularly some antidepressants. Some medicines can occasionally cause increased sweating which may be extreme.
- Some medical conditions. Some conditions can cause occasional or constant heavy sweating which is usually, but not always, generalised. Examples are:
- Having blood sugar (glucose) which is higher than normal (diabetes).
- Heart valve infection (endocarditis).
- Generalised anxiety disorder.
- An overactive thyroid gland (hyperthyroidism).
- Cancer of the blood (leukaemia).
- Cancer in the cells of the body's lymphatic system (lymphoma).
- Tuberculosis infection.
- Excess sweating can also occur for very little obvious reason.
What is hyperhidrosis?
Hyperhidrosis is excessive sweating to an extreme degree. There are no guidelines defining what normal sweating is, so hyperhidrosis is defined by the way in which sweating affects your life. You have hyperhidrosis if:
- You avoid physical contact with others because you are worried about your sweat.
- You avoid certain activities because they will make you sweat
- Sweating is interfering with work or leisure activities - for example, hands being too wet to type.
- You spend a lot of time dealing with excessive sweating - for example, changing shoes and socks throughout the day.
Hyperhidrosis usually stops when you are sleeping, unlike the medical causes of sweating listed above. It is thought that hyperhidrosis is a condition in which sweat glands are overactive, or overly responsive, to small stimuli. Those affected may produce several times the normal quantity of sweat, which can be embarrassing, uncomfortable and distressing. Up to 3% of people are believed to suffer from hyperhidrosis. See separate leaflet called Excessive Sweating (Hyperhidrosis) for more details.
What makes sweating feet smell?
Sweat doesn't smell bad when it's produced. However, if sweat remains on skin (such as when it can't evaporate in warm conditions - for example, when trainers with non-'breathable' linings are worn), skin germs (bacteria) break down the sweat. This produces the characteristic smell of sweaty feet. We probably all remember this smell from school changing rooms.
Sweat is more likely to become smelly if:
- You are on your feet all day, particularly in a warm environment.
- You are under a lot of stress.
- Your shoes are tight so sweat can't evaporate.
- Your shoes are made of material that doesn't allow sweat evaporation.
- Poor hygiene can play a part too, as washing your feet infrequently or not changing socks can allow bacteria to thrive.
How can I reduce foot sweating and smell?
- Wash feet daily with soap and water and dry thoroughly - especially between the toes where skin can easily become soggy and bacteria can breed.
- Keep toenails short and clean.
- Remove hard skin from the soles of your feet - it can become soggy when damp, becoming a place for germs (bacteria) to grow.
- Wear fresh socks every day.
- Alternate your shoes daily to allow them to dry thoroughly. Airing insoles can help.
- Wear absorbent socks made of natural fibre, or socks designed to absorb moisture.
- Avoid shoes made of synthetic material.
Avoid tight-fitting shoes - aim for shoes which allow air to circulate, including sandals and open-toed shoes.
- Antiperspirant reduces sweating from the eccrine glands by mechanically blocking the sweat ducts. Antiperspirant consists mainly of various aluminium salts dissolved in alcohol and mixed with essential oils. Strong antiperspirants for excessive sweating (hyperhidrosis) containing aluminium chloride are available over the counter.
- Dab your feet with cotton wool dipped in surgical spirit - this helps dry out the skin (but will sting on any cracks).
- Use an antifungal foot spray or powder at night.
- Use medicated insoles, which act as deodorant.
- Use antibacterial soap for feet, available from pharmacies.
What are the complications of excess foot sweating?
- Excessively sweaty or smelly feet are socially embarrassing and can cause enormous distress to those affected.
- This can include young people, who may become socially isolated and avoid useful activities as a result.
- Increased dampness of the feet also increases the chance of foot infections such as athlete's foot, and of cuts to and breaks in the skin, leading to other infections.
- In people with other conditions which put the feet at risk, such as diabetes, peripheral neuropathy and peripheral arterial disease, excess sweating (hyperhidrosis) can contribute to the risks of foot infection leading to more serious conditions such as a skin infection (called cellulitis) and ulceration.
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