Read more: 鈥�Secrets of the body鈥�
YOUR skin is home to 5 million sweat glands. Apart from the lips 鈥� and the head of the penis in men 鈥� each square centimetre has 200 on average. The majority secrete mostly water and salt, and mainly serve to cool you down. These are your eccrine glands. But you also have another sort called apocrine sweat glands. It is these you can thank for your personal aroma.
Located in hairy areas 鈥� especially the armpits, which contain around 50 each, and groin 鈥� apocrine glands secrete an oily substance composed largely of proteins and fats. We have these glands at birth but they do not kick in until puberty. Even then, sweat on its own has no aroma. Your distinctive bouquet emerges only when it meets the thriving community of bacteria on the skin.
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Skin microbes break down the nutrients in sweat into volatile organic compounds with an array of familiar pungent smells. Notable among these are the vinegary whiff of propionic acid, and the 鈥渞ipe鈥� aroma of isovaleric acid, also found in cheeses.
Genetics, environment and diet all influence the way you smell. Spicy foods, garlic and red meat tend to boost body odour for the worse. Vegetarians tend to smell least offensive. Some odours can even be a warning sign of illness: fruity or sweet smells may indicate diabetes, for example, while an antiseptic, bleach-like smell could be a sign of liver disease.
So distinctive are our personal aromas that families can identify siblings, parents or children by body odour alone. However, we tend to prefer the scent of strangers to those who smell like us, which may be an evolutionary adaptation to avoid incest. Our aromas offer other clues too. Just by sniffing someone, we can identify personality attributes, including neuroticism and dominance. One study found that women prefer the smell of dominant men. Another has shown that men find women鈥檚 body odour most appealing when they are at the most fertile period in their menstrual cycles (快猫短视频, 17 September 2011, p 44).
鈥淛ust by sniffing someone, we can identify personality traits鈥�
While many people would like to expunge their personal aroma, some have none to begin with. Recent research has identified the gene that controls body odour (as well as whether or not you tend to have wet or dry type earwax). In most Europeans and Africans, this ABCC11 gene is switched on, resulting in a surge of stinkiness with the onset of puberty (Journal of Investigative Dermatology, vol 130, p 529). However, about 2 per cent of Europeans and almost all people from eastern Asia carry two copies of the recessive allele for this gene. As a result, they produce no apocrine sweat and lack eau de underarm altogether.
This article appeared in print under the headline 鈥淎 nose knows鈥�