Sweaty Feet

Why do feet sweat?

Sweating is normal. It has three main 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 away from predators or any other threat.

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.

(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.)

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 (sweat) a day. Sweat glands are more concentrated on the feet (there are more sweat glands per inch of skin) 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 produced 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.

What causes excessively sweaty feet?

Excessive sweating of the feet is commonly caused by:

• 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. Excessive foot sweating can be brought on by anxiety or emotional stress.
• Eating (this usually mainly affects the head and neck).
• Damage to the sympathetic nerves. These are a special set of nerves involved in stress responses and can be damaged due to trauma or to medical conditions such as diabetes.
• Footwear. Some shoes and socks can increase the amount of sweat produced and may prevent it from evaporating (eg, socks made from man-made fibres or plastic shoes).
• Being on your feet all day. Sweaty feet are more common in people who stand 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 and this is called plantar hyperhidrosis. See the separate leaflet called Hyperhidrosis (Excessive Sweating) for more information about this condition.
• Some prescribed medications - Some medicines, particularly some antidepressants, can occasionally cause increased sweating .
• 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.

Why does sweating make feet smelly?

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.

Sweating is normal, but nobody wants stinky feet. Sweat is more likely to become smelly if people are:

• On their feet all day, particularly in a warm environment.
• Under a lot of stress.
• Wearing shoes that are tight so sweat can't evaporate.
• Wearing shoes that are made of material that doesn't allow sweat evaporation.

• Poor hygiene can play a part too - for example, washing feet infrequently or not changing socks can allow bacteria to thrive.

How to stop sweaty feet

Fortunately there are lots of remedies and strategies which can help to stop smelly sweaty feet.

Foot care strategies

• Washing feet daily with soap and water and drying thoroughly - especially drying carefully between the toes where skin can easily become soggy and germs (bacteria) can breed.
• Making sure that feet are dry before putting socks and shoes on.
• Keeping toenails short and clean.
• Removing hard skin from the soles of the feet - this can otherwise become soggy when damp, becoming a place for germs to grow.

Socks to reduce sweaty feet/smelly feet

• Wearing fresh socks every day.
• Changing socks more than once a day if necessary, particularly after exercise which caused sweating or after walking a long way.
• Wearing absorbent socks made of natural fibre or socks designed to absorb moisture. Socks made of wool, cotton or a mixture of these are thought to be the best socks to reduce smells if someone has particularly sweaty feet.
• Avoiding nylon socks.
• 'Sports socks' are often designed to absorb sweat.

Shoes to reduce sweaty feet/smelly feet

• Avoiding shoes made of synthetic material.
• Avoiding tight-fitting shoes, aiming for shoes which allow air to circulate, including sandals and open-toed shoes.
• Alternating your shoes daily to allow them to dry thoroughly.
• Airing or alternating insoles can help.

Foot products which might help smelly or sweaty feet

• Antiperspirants reduce sweating by mechanically blocking the sweat ducts and can be used on feet Antiperspirants consist 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. These come as a roll-on solution, spray or dusting powder. They are used once a day until the problem improves (usually for about a week), then as needed.
• An antifungal foot spray or powder at night can help.
• Medicated insoles which act as a deodorant (reducing odours).
• An antibacterial soap , available from pharmacies, can be used particularly on the feet. (For example, Hibiscrub®.)

Other treatments

For people with excessive sweating (hyperhidrosis) or sweaty feet (plantar hyperhidrosis), a treatment called iontophoresis is occasionally used. This is a treatment that uses electrical stimulation. This is normally a procedure done in a private specialist clinic, but home treatment kits are available, although they are quite expensive. You can read more about this treatment in the separate leaflet called Hyperhidrosis (Excessive Sweating).

Botox injections can be used for excessive sweating. These are not generally available on the NHS but can be accessed through private clinics. Evidence is not clear and they may not be as beneficial for sweaty feet as they can be for excessive sweating in other parts of the body.

Complications of sweaty feet

• Excessively sweaty or smelly feet can be 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.