Science could make deodor­ant ob­so­lete

Science Illustrated - - FRONT PAGE -

Sweat is a daily nui­sance to many peo­ple, but to some, the mois­ture and smell is in­val­i­dat­ing. Now, doc­tors can re­duce the sweat pro­duc­tion us­ing mi­crowaves and get rid of bad smells by trans­fer­ring sweat from an­other per­son.

The man has not washed his armpits for days. His old sweat gives nour­ish­ment to mil­lions of bac­te­ria, which re­pro­duce un­con­trol­lably. The doc­tor takes a spat­ula, presses it against the man’s armpit and scrapes off a mix­ture of dead skin cells, bac­te­ria and sweat. Then, she asks an­other per­son – the pa­tient – to lift his arm and wipes it all off in his armpit.

This treat­ment may sound re­pul­sive, but even a few days later, the pa­tient will prob­a­bly thank both the doc­tor and the sweaty man. The bac­te­ria from the donor’s armpits are be­nign and will not make the sweat smell badly, and right now, they are work­ing hard to set­tle in the pa­tient’s armpits. Within a short time, they will have won over the per­son’s own bac­te­ria, which made his sweat smell, and this marks the end of the hu­mil­i­a­tion of see­ing peo­ple turn­ing up their noses and pulling away.

The so-called sweat trans­plant is just one of sev­eral new meth­ods to treat pro­fuse sweat­ing. The bad smell is fought us­ing good bac­te­ria, and the amount of sweat can be re­duced us­ing nerve poi­son and mi­crowaves. Most re­cently, Chi­nese sci­en­tists have dis­cov­ered a gene, which may give new knowl­edge about sweat and be the key to new and more ef­fi­cient treat­ments of sweat.


Sweat is cru­cial for our sur­vival, as this is the most im­por­tant way we reg­u­late our body tem­per­a­ture. Un­der a scorch­ing sun, or work­ing out in the fit­ness cen­tre, the body gets warm and be­gins to pro­duce sweat. When the sweat lies on the skin, the body heats it up, mak­ing it evap­o­rate. Thus, the sweat takes the heat up into the air, and the body is cooled down. If, how­ever, you wipe off the sweat with a towel, or it drips off by it­self, no evap­o­ra­tion takes place, and thus no cool­ing. As a re­sult, the body pro­duces more sweat in an at­tempt to keep down the body tem­per­a­ture.

Sweat pro­duc­tion is con­trolled, among other things, by a small area in the lower part of the brain called the hy­po­thal­a­mus. This area works as a kind of ther­mo­stat, which mea­sures the tem­per­a­ture of the blood that flows through the brain. If the tem­per­a­ture is too high, the hy­po­thal­a­mus sends out nerve sig­nals to the 2-4 mil­lion sweat glands, which can be found in the skin prac­ti­cally all over the body – they are only miss­ing on the lips, the fore­skin and labia mi­nora as well as glans on the pe­nis and cli­toris. The nerve sig­nal cause the sweat glands to pro­duce sweat.

But it is not only the in­creased body tem­per­a­ture that makes us sweat. Stress, anx­i­ety, ner­vous­ness, pain and other strong, neg­a­tive feel­ings make the lim­bic sys­tem in the brain ac­ti­vate the sweat glands. We talk about “the cold sweat of anx­i­ety” or about “break­ing a sweat”, and most peo­ple have ex­pe­ri­enced get­ting sweaty palms in a stress­ful sit­u­a­tion, e.g. on a first date.

The rea­son is de­bated, but slightly damp palms may serve to give us a bet­ter grip, and from an evo­lu­tion­ary per­spec­tive, this may have been an ad­van­tage in stress­ful sit­u­a­tions when our an­ces­tors were hunt­ing wild an­i­mals or climb­ing rocky slopes. But when sweat­ing be­comes ex­ces­sive, the sweaty palms have the ex­act op­po­site ef­fect.


At­tacks of sweat­ing caused by emo­tions hap­pen au­to­mat­i­cally and can­not be con­trolled con­sciously. The po­lice, e.g. in the US, have learned to use this. Some­times, the au­thor­i­ties use lie de­tec­tors, which mea­sure the amount of sweat from the sus­pect’s palms and fin­ger­tips etc. dur­ing ques­tion­ing. An un­truth­ful an­swer to a ques­tion like “Did you shoot your girl­friend?” will un­avoid­ably trig­ger a stress re­ac­tion, which will make the sweat break.

In prin­ci­ple, lie de­tec­tors are very re­li­able, as it is al­most im­pos­si­ble to lie with­out in­creas­ing your sweat pro­duc­tion. One prob­lem is that the sweat may also be caused by fear of a wrong­ful con­vic­tion.


Many of us are fa­mil­iar with the un­pleas­ant smell of sweat and wet patches un­der our arms, and stud­ies have shown that more than one in five con­sider their own body odour to be a prob­lem. For most, a deodor­ant is enough to limit the prob­lem, but for some, not even the most ef­fi­cient deodor­ant can con­trol the odour. Oth­ers sweat in ex­treme amounts – not only from their armpits, but also from e.g. their palms or their fore­head – and are soaked by their own sweat and have to change clothes sev­eral times a day. In some 3 % of the pop­u­la­tion, or al­most 200,000 Danes, the prob­lem is so se­ri­ous that they are di­ag­nosed with hyper­hidro­sis by their doc­tor, i.e. ab­nor­mally in­creased sweat pro­duc­tion. These peo­ple ex­crete four to five times as much sweat as nor­mally.

An aver­age per­son typ­i­cally ex­cretes 0.5-2 litres of sweat dur­ing a day, but in case of hard, phys­i­cal work and high tem­per­a­tures, we may sweat just as much in just one hour. The Amer­i­can marathon run­ner Al­berto Salazar holds the un­of­fi­cial world record in sweat­ing. As part of his prepa­ra­tions for the Olympic Games in Los An­ge­les in 1984, he ex­er­cised in a cli­mate room to pre­pare for the in­tense heat and strong sun, which were ex­pected on the day of the marathon. Dur­ing the train­ing ses­sions, sci­en­tists mea­sured a sweat pro­duc­tion of 3.06 l/h, and dur­ing the marathon it­self, Salazar pro­duced 5.43 kg sweat, 8.1 % of his body weight.

In peo­ple suf­fer­ing from hyper­hidro­sis, the sweat glands ex­crete con­sid­er­ably more sweat than nor­mally for no ap­par­ent rea­son. This con­di­tion can be very dis­turb­ing, as the con­stantly wet skin may lead to de­hy­dra­tion and chronic in­fec­tions, and also, it may feel shame­ful to many peo­ple if they con­stantly have to wipe their palms or change shirts. The prob­lem also has a self-re­in­forc­ing ef­fect, as if you get stressed by sweat­ing pro­fusely, this will trig­ger nerve sig­nals from the brain, which will make the sweat run even faster. This may cause an evil spi­ral, which af­fects your emo­tional life and causes so­cial in­hi­bi­tion.

Sci­en­tists do not know the ex­act rea­son for the con­di­tion, which is pre­dom­i­nant in

girls. The con­di­tion usu­ally oc­curs in child­hood and wors­ens in pu­berty, and it may last through­out a per­son's life. Some be­lieve that a de­fect in the ner­vous sys­tem leads to over­ac­tive sweat glands, while oth­ers think that the con­di­tion is due to an im­bal­ance in the hor­mone pro­duc­tion. In 2016, Chi­nese sci­en­tists dis­cov­ered a gene, which may be the trig­ger­ing fac­tor.

Sci­en­tists have known for a long time that hyper­hidro­sis is, to a cer­tain ex­tent, hered­i­tary. Some 3 % of the pop­u­la­tion are suf­fer­ing from this con­di­tion, but if mem­bers of your near­est fam­ily suf­fer from hyper­hidro­sis, your risk of be­ing af­fected your­self in­creases by 50 %. Yuan-Rong Tu and his col­leagues from Fu­jian Med­i­cal Univer­sity in Fuzhou, China, sus­pected the gene AQP5, which cre­ates a wa­ter chan­nel in the mem­brane of the sweat-pro­duc­ing cells. The sweat lit­er­ally flows through this chan­nel, and the sci­en­tists’ hy­poth­e­sis was that peo­ple suf­fer­ing from hyper­hidro­sis may cre­ate more wa­ter chan­nels than other peo­ple.

When com­par­ing the num­ber of wa­ter chan­nels to the ac­tiv­ity of the AQP5 gene in 30 peo­ple, where some were suf­fer­ing from hyper­hidro­sis and oth­ers were healthy, the the­ory held wa­ter. In the pro­fusely sweat­ing hyper­hidro­sis pa­tients, the AQP5 gene was three times as ac­tive as in the healthy peo­ple, and the pa­tients had more than twice as many wa­ter chan­nels in their sweat glands.


The Chi­nese sci­en­tists will now ex­am­ine whether a spe­cial mu­ta­tion in the AQP5 gene makes the sweat-pro­duc­ing cells cre­ate more wa­ter chan­nels. This knowl­edge may be used to de­velop drugs, which can re­duce the ac­tiv­ity of the gene, so that the cells will cre­ate less wa­ter chan­nels and hope­fully re­duce the ex­cre­tion of sweat. Doc­tors are al­ready us­ing a num­ber of treat­ments, which in each their way re­duce the amount of sweat. Sweaty hands and feet may e.g. be bathed in wa­ter baths with a weak elec­tric cur­rent. Ac­cord­ing to one the­ory, this re­places the salt ions on the skin, elec­tri­cally charged mol­e­cules, with alu­minium ions,

which dampen the sweat pro­duc­tion. The ef­fect will last for a cou­ple of weeks.

An­other well-doc­u­mented treat­ment is Botox in­jec­tions – which are also used to smooth out wrin­kles – in the palms or armpits, for ex­am­ple. Botox is a nerve poi­son, which pre­vents the nerve sig­nals from the brain to ac­ti­vate the sweat glands. The ef­fect lasts for up to six months. In an­other treat­ment, sweat glands in the armpits are fried lightly by send­ing mi­crowaves into the skin.


Ir­re­spec­tive of whether you sweat pro­fusely or just a lit­tle, you are equally sub­ject to the other ma­jor dis­ad­van­tage of sweat­ing – the bad odour. Para­dox­i­cally, sweat in it­self does not smell, and two con­di­tions must be met to cre­ate the char­ac­ter­is­tic odour. First of all, the sweat must come from the apoc­rine sweat glands, which are pri­mar­ily found in the armpits and crotch. They ex­crete a spe­cial kind of sweat, which – in ad­di­tion to the nor­mal salts also con­tain or­ganic mol­e­cules like lac­tic acid and urea. Se­condly, these sub­stances must be bro­ken down by bac­te­ria and con­verted into foul-smelling catabolic prod­ucts, be­fore the sweat be­gins to smell.

The com­po­si­tion of the un­der-arm bac­te­ria varies from per­son to per­son. Of the bac­te­ria, which thrive in the armpits, three types in par­tic­u­lar make the sweat smell: Sta­phy­lo­coc­cus, Co­rynebac­terium and Anaero- coc­cus. Each has its own char­ac­ter­is­tic smell.

In 2013, the Bel­gian doc­tor Chris Calle­waert from Univer­sity of Cal­i­for­nia, San Diego, USA, showed that the bac­te­rial flora in the armpits of nine test sub­jects were very dif­fer­ent. This gave him the idea for an ex­per­i­ment, which was pub­lished in 2016.

Calle­waert used 18 pairs of close rel­a­tives, of whom one had se­ri­ous prob­lems with bad armpit smell, while the other one had a more neu­tral smell. He scraped off some of the bac­te­rial flora from the nice-smelling peo­ple’s armpits and smeared the armpits of the foulsmelling rel­a­tives. A panel of odour ex­perts with a very good sense of smell was then asked to reg­u­larly smell the test sub­jects’ armpits. The re­sults were very con­vinc­ing. In 16 of the 18 pairs, the rel­a­tive with the stinky armpits ex­pe­ri­enced a sig­nif­i­cant im­prove­ment in his or her smell af­ter just a few days. The ef­fect re­mained for at least three months.

How­ever, be­fore you be­gin smear­ing your­self with an­other per­son’s sweat, it may be a good idea to put a cot­ton bud into your ear and see what comes out. If your ear­wax is hard and dry, you prob­a­bly do not have to worry at all about the smell from your armpits. Then you have a ver­sion of the ABCC11 gene, which not only pro­duces this type of ear­wax. It is also re­spon­si­ble for en­sur­ing that the sweat from the apoc­rine sweat glands has a low con­tent of the sub­stances that trans­form the bac­te­ria to stink­ing mol­e­cules. This ge­netic vari­ant is com­mon in the East, where prob­lems with body odour are gen­er­ally less out­spo­ken than in the West. Here, ear­wax is typ­i­cally soft and wet, which is con­nected to more sweaty armpits.

When we lie, ner­vous­ness will make us sweat more. So a lie de­tec­tor mea­sures how much the sus­pect sweats from his fin­gers.

Bac­te­ria around a sweat pore live off nu­tri­ents in the sweat. Some types of bac­te­ria have waste prod­ucts, which smell badly.

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