Everything you ever wanted to know about sweat

THE_IMAGINARIUM_TEXT

Today it is approaching 35 °C in Berlin and I am sweating profusely. Someone once said:

men perspire, but women glow.

That someone has never seen a cranky Swedish woman navigating through the Berlin traffic jams at 12 noon on her bike, in full sun and at 35 °C. I must confess that some German profanities might have slipped my tongue. However, cursing at each other is a sport in Berlin, a sport I full-heartedly participate in.

Despite having “glowed” so abundantly for several hours, I still do not stink. I smell a bit salty and the lab dog think that my feet taste great. In contrast, before the submission of my Ph.D.-thesis I stank all the time despite not sweating much, showering regularly and changing shirts one to two times per day. What is the deal with this? Is sweat not always sweat? Why does some sweat seem to smell more than other types?

Sweat droplets. By Mgodiseo (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 4.0-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/4.0-3.0-2.5-2.0-1.0)], via Wikimedia Commons

Sweat droplets. (Image credit: Bibikoff)

The basics of sweat

We perspire (sweat) through glands called sweat glands that are located in our skin (which you probably already have noticed). We have about 2-4 million sweat glands and women actually have more of them than men. However, men’s sweat glands are more active.

The main reason for sweating is the so called thermoregulation. Thermoregulation is the process by which the body regulates its temperature. We sweat, the skin becomes wet and the evaporation process removes excess heat energy from the body.

Obese people tend to sweat more simply due to the larger body volume that has to be cooled down (the area/volume ratio is low). However, the fitter you get, the faster you will begin to sweat during exercise since your body has been trained to start the biological air conditioning ASAP.

Children cannot sweat as much as adults and are hence much more heat sensitive. This is good to think about before bringing your kids to the sauna. Dogs hardly sweat at all and have to thermoregulate by panting. Your dog is very, very sensitive to heat.

Please, do not leave your child or your dog in the car. It can be a death trap.

We can sweat as much as 10-14 L per day under extreme conditions, but more normal maximum rates are around 2-4 L. 14 L is quite a lot of sweat!

Why do we sweat?

The reason we sweat is first and foremost due to the above mentioned thermoregulation: We sweat to cool the body down during heat or exercise.  However, we can also start sweating when we are stressed or when we have consumed food and/or beverages such as coffee, alcohol, garlic and spicy food (gustatory sweating). Other things that can cause sweating are the menopause, several types of medications (for example thyroid hormones) and withdrawal from narcotics.

Thermoregulatory sweat generally appears on the entire body whereas stress-induced sweat often is localized to the armpits, palms, forehead and the feet. This, I can confirm from my stressful experience called Ph.D.

Sweat lodge. By Mgodiseo (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 4.0-3.0-2.5-2.0-1.0 (http://creativecommons.org/licenses/by-sa/4.0-3.0-2.5-2.0-1.0)], via Wikimedia Commons

Sweat lodge.
(Image credit: Mgodiseo)

Different sweat glands

As it turns out there are different sweat glands producing the summer-in-Berlin-sweat compared with the frustrated-PhD-sweat.

The eccrine glands can be found all over your body and produce pretty much odorless sweat. This sweat only starts to smell after a few days when a highly diverse microbial mat has colonized your skin.

The so called apocrine glands are found in your groin, armpits and scalp. The sweat produced by these glands contains more fat than the sweat produced by the eccrine glands and has a very personal smell.  Also, due to the high fat content (and other compounds) of this sweat, the skin bacteria quite enjoys it and will rapidly produce a ripe smell, also known as body odor (BO). The most common compound of BO is buturic acid, a small molecule that is produced by bacteria such as Corynebacteria during break-down of fatty acids. In addition, break-down of several types of amino acids can also result in odor such as propanoic acid. Furthermore, 3-methyl butanoic acid is a component of several ripe cheeses and can also be present in BO as a side product by the bacterium Staphylococcus epidermis.

IMG_7613

Dr. Anna sweating though the eccrine glands.

 

The apocrine glands can also excrete compounds like garlic smell from the food we consume as well as several hormonal components and pheromones.

Ok, time to pick up the spawn from school, drag the dog though the shadows and have a well-deserved glass of ice cold white wine! I’ll shower tonight.

I wish you a happy weekend!

Science Safely!

Dr. Anna of The Imaginarium

...is sweating profusely right now.

…is sweating profusely right now.

Lab dog hates heat.

Lab dog hates heat.

References

Sawka, M. L.; Wenger, C. B.; Pandolf, K. B. (1996). “Thermoregulatory responses to acute exercise-heat stress and heat acclimation”. In Fregly, M. J.; Blatteis, C. M. Handbook of Physiology. Section 4: Environmental Physiology. New York: Oxford University Press. ISBN 0-19-507492-0.

http://www.nlm.nih.gov/medlineplus/ency/anatomyvideos/000127.htm

Mack, G. W.; Nadel, E. R. (1996). “Body fluid balance during heat stress in humans”. In Fregly, M. J.; Blatteis, C. M. Handbook of Physiology. Section 4: Environmental Physiology. New York: Oxford University Press. pp. 187–214. ISBN 0-19-507492-0.

Kameia, Tomoya; Tsudab, Takao; Kitagawab, Shinya; Naitoha, Ken; Nakashimaa, Koji; Ohhashi, Toshio (June 1998). “Physical stimuli and emotional stress-induced sweat secretions in the human palm and forehead”. Analytica Chimica Acta 365 (1–3): 319–326.

Posted in Bacteria, Biology, Medicine, The Biology of Disgusting and tagged , , , , .

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