Sweat smells bad, stains clothes and embarrasses us in public. But it’s vital to health, keeping our bodies cool during exercise, on a sunny day or when we eat certain foods such as chilli.
We also produce sweat when we feel under pressure, as part of our stress response.
Here, the experts reveal the latest understanding about sweat’s role in health — and how to keep it under control.
WE PRODUCE TWO TYPES OF SWEAT
We have nearly four million sweat glands in our skin which produce up to 25 ml of sweat an hour to regulate our body temperature — this can rise to two to four litres an hour during exercise, says George Havenith, a professor of environmental physiology and ergonomics at Loughborough University.
We can produce two to four litres of sweat an hour during exercise
Almost two million people in the UK suffer from excessive sweating or hyperhidrosis. ‘They can’t function normally: they have to change their shirt every hour or can’t shake hands with people,’ says Dr Anton Alexandroff, a consultant dermatologist at the University Hospitals of Leicester NHS Trust.
We’re losing moisture through our skin all the time, but don’t notice because the air makes most of the liquid evaporate quickly, says Professor Havenith.
‘People who say they don’t sweat are wrong,’ he adds. If we didn’t sweat we would collapse and die half an hour into a run as our body temperature would rise too much.
‘The difference in sweat levels lies in how sweat is distributed between glands: some people feel it extensively as it all comes out of one area, for example the forehead.
‘In people who say they don’t sweat, the perspiration is just more evenly distributed across glands, so doesn’t build up a layer of liquid that they notice,’ he explains.
We produce two types of sweat — the watery sweat that cools us down, and an oily liquid that may be linked to sexual attraction.
Cooling sweat is produced by the eccrine glands, found just under the skin all over the body. When our body heats up, the hypothalamus, the temperature centre of the brain, instructs these glands to produce sweat: this evaporates on the skin, taking heat from our bodies.
We produced sweat the cools us down and an oily liquid that may be linked to sexual arousal
We produce seven times more watery sweat than the oily kind because of its role in protecting us from overheating, says Dr Justine Hextall, a consultant dermatologist at Western Sussex Hospitals.
This sweat is produced by filtering fluid in the eccrine glands. ‘Salts are extracted back into the blood if they are needed and the remaining salty liquid passes out as a fluid onto the skin,’ explains Professor Havenith.
WHY TEENAGERS CAN BE SO STINKY
The second type of sweat is produced by the apocrine glands in the armpits, genitals and nipples. They produce an oily liquid full of fat and protein — animal studies suggest this sweat contributes to sexual attraction.
Though it’s odourless when released, once this sweat is on the skin it reacts with bacteria such as Staphylococcus hominis, producing malodorous by-products.
‘A hairy armpit has a big surface for debris and bacteria to adhere to so tends to be more smelly,’ says Professor Havenith.
Teenagers’ sweat glands tend to smell more because of their fluctuating hormones
People from east Asia typically don’t have body odour because they have a gene that means they don’t produce certain proteins that would be converted by bacteria into odours, he adds.
This type of sweat can be triggered by hormones such as cortisol, and is released at times of stress or extreme emotion. It’s part of our fight or flight response. ‘A small amount of sweat on our hands and feet improves the friction in our skin and helps us grip,’ says Professor Havenith.
Teenagers’ sweat tends to smell because their fluctuating sex hormones stimulate the apocrine glands to release oily sweat,’ says Dr Hextall. ‘Because of the habits teens tend to have — such as not washing — odour-causing bacteria builds up.’
YOUR UPBRINGING AFFECTS SWEAT
Some sweat glands are more active than others. One theory is that heat exposure before the age of four determines how well your glands cool you down, says Professor Havenith.
‘That’s why people who grow up in the tropics sweat more than those who holiday there, because more glands are active and these activated glands are also more efficient at cooling the body down, producing more sweat.’
Having a tattoo might also make you sweat less, as the inking damages sweat glands, according to a study published earlier this year in the journal Medicine and Science in Sports and Exercise.
TAKE HOT BATHS BEFORE HOLIDAYS
To reduce excessive sweating on holiday, prepare your body weeks before as athletes do, says Professor Havenith.
Prepare your body weeks before going on holiday to avoid excessive sweating
Before an event in a hot climate, many train their sweat glands to work efficiently in high temperatures by working out in hot rooms. ‘Using a sauna or having a hot bath regularly can train your sweat glands to be more efficient at high heat, producing more sweat to cool you down, but distributing it better all over the body,’ he says.
WHY THE PLUMP SWEAT MORE
In general, overweight people sweat more, says Dr Alexandroff. They have to exert more energy when exercising to move their weight and they have a bigger surface area to cool down.
The more fat a person has, the harder it is to cool down and the more sweat they need to produce, adds Dr Hextall.
Fit people also sweat a lot during exercise because their bodies have adapted to be more sensitive to temperature change and are more efficient at sweating to keep the body cool, says Professor Havenith.
ANTIPERSPIRANT GOES ON AT NIGHT
If you shower daily you’ll remove bad bacteria so you shouldn’t smell, says Dr Alexandroff. Another trick is to use antiperspirant before bed. Women who do this have been shown to sweat less than those who use the products first thing in the morning.
Antiperspirants generally contain aluminium chloride. Aluminium particles are taken up by cells in the sweat glands, causing them to swell and close up so they no longer release sweat. It is thought that by applying it at night the antiperspirant has time to ‘set’ in the pores during sleep.
Dry your armpits and apply antiperspirant at night, says Dr Hextall. ‘What’s left on the skin will irritate some people so in the morning, have a shower.
‘You can apply a deodorant for fragrance — even rub lemon juice into your armpits: studies suggest this can change the pH of skin so that some odour-causing bacteria that prefer alkaline environments don’t survive,’ she adds. (Some experts have suggested aluminium may be linked to breast cancer, but this remains controversial.)
HAVE HOT DRINKS TO COOL DOWN
Some people sweat more when eating foods such as peanut butter — this is thought to be a mild allergic reaction. ‘The body may perceive certain triggers as harmful and flush them out through sweat,’ says Professor Havenith.
Hot coffee or tea can also make you sweat as it stimulates temperature sensors in the body, which set off your body’s cooling mechanism. And caffeine can stimulate the nervous system to activate sweat glands.
Tea makes you sweat more by stimulating the temperatures sensors in the body
In fact hot drinks may be better at cooling you down than ice cold ones, says Professor Havenith: ‘We produce more sweat in response to a hot drink than with a cold drink, which actually suppresses sweating and doesn’t change our body temperature.’
Chilli makes us sweat because it contains capsaicin, a chemical that stimulates nerves in the skin and mouth that detect heat. ‘Body temperature hasn’t changed, but the nervous system has been fooled by these chemicals,’ explains Professor Havenith.
YOU SWEAT WHAT YOU EAT
What you eat can affect sweat odour. Garlic or asparagus can give off a pungent odour because chemicals in these foods are not broken down and are released in breath and sweat, says Dr Alexandroff.
BEING SMELLY MAY PROTECT YOU
Diabetes and other metabolic conditions can alter body odour. This is because they lead to a build-up of toxins in the blood which are transmitted to the sweat, which can then be detected as acidic or rotten apple scents, explains Professor Havenith.
Patients may also have nerve damage as a result of uncontrolled blood sugar levels. This in turn can affect the nerves surrounding sweat glands, and cause them to sweat excessively, says Dr Hextall.
The upside to the odour is that you’re less likely to be bitten by a mosquito, according to a 2005 study by Rothamsted Research and the University of Aberdeen. Scientists found people who don’t get bitten produce chemicals that ‘mask’ the scent of lactic acid, a bodily waste product that attracts mosquitoes.
A high-protein diet can also lead to malodorous sweat, particularly if you’re exercising, adds Dr Hextall. ‘If you don’t have enough carbs your body will start to break down protein as fuel, which releases ammonia in sweat, leading to an ammonia-like smell.
‘This scent could also indicate that the liver or kidneys aren’t working properly.’
MEN AND WOMEN SWEAT THE SAME
The traditional theory is that men sweat more. But a study by the University of Wollongong in Australia suggested sweating is linked to body size. Smaller people, regardless of gender, increase blood circulation to their skin to lose heat, rather than sweating.
TRY A SWEAT TRANSPLANT
For some, the issue is not down to excess sweat but the wrong type of bacteria on their skin causing excess odour. Earlier this year researchers at the University of California suggested a treatment for this: a ‘bacterial transplant’.
Scientists studied identical twins, one with body odour, the other without. They took a swab of bacteria from the fresh-smelling twin and smeared it into the armpit of the smelly one. The odour disappeared, even a year later. The theory is that the new bacteria outnumbered the bad, eliminating the odour.
‘It is like a probiotic that improves odour,’ says Dr Alexandroff.