Do Chinese lack sweat glands in their armpits? Why does spicy food make you sweat?
A good friend of mine, a Chinese born in Nanking, China, told me that many Chinese (including himself) do not need to use deodorant. "We don't have sweat glands under our arms," he said, "We don't need to use deodorant." I'd always thought that all humans were endowed with similar glands and organs. We all have lungs, livers, hearts, lymph glands, etc. Is Mr. Fu wrong? He's rarely wrong about anything, honest. --Marshall
Why does spicy food make you sweat?
Mr. Fu exaggerates, but he's not completely wrong. It's not that Asians don't have sweat glands under their arms; the difference is that they have markedly fewer apocrine glands than black or white people. That doesn't mean they sweat less--eccrine glands, the other main type of sweat gland, are a thousand times more numerous on most bodies, and Asians have plenty of them. But apocrine glands are the kind that make you stink.
Those lucky Asians, you may say--but every silver lining has its cloud. For Asians it's osmidrosis. Technically osmidrosis is the production of objectionably aromatic sweat, but many Asians think they've got a problem if they produce any odor when sweating--even an amount that would be considered normal in other races. Of the 22 articles about osmidrosis that turned up in a recent on-line search, virtually all were by Asian doctors. Unlucky Asians who do produce fragrant sweat may be shunned socially, and those who can afford it often seek medical help. Treatment can be pretty drastic. Typical medical journal headline: "Axillary [armpit] osmidrosis treated by partial removal of the skin and subcutaneous tissue en bloc and apocrine gland subcision." The technology used ranges from ultrasound and lasers to more primitive devices. (One abstract reads in its entirety: "Shaving off the sweat glands and hair follicles with a single-use safety razor is described.") Complications, according to one report, occur in roughly 7 percent of cases--not bad compared to, say, penile-lengthening surgery, but high for a problem that other ethnic groups solve with Right Guard.
Why are Asians different? Nobody knows, but it's tempting to credit the same evolutionary force thought to be responsible for the epicanthic fold--namely, adaptation to cold. Your columnist thought he was on to something when he learned that Eskimos produce much more facial sweat and less body sweat than Caucasians, presumably because the face is the only area that can efficiently shed excess heat if you're bundled up in heavy clothing. But then I remembered that the nonsmelly eccrine glands produce the lion's share of the moisture in sweat, that sweat production varies considerably even among Asians, etc. So it's back to the lab.
On the subject of sweating after eating spicy food, what we're talking about is called gustatory sweating. It's usually confined to the face and is triggered by tasting (or sometimes merely seeing or smelling) spicy food. Many people experience mild sweating on the upper lip or nose; a few with a pathological response known as gustatory hyperhidrosis perspire profusely on one or both sides of the face. Gustatory sweating is thought to be a side effect of the reflex that makes you salivate. The nerves connected to the salivary glands produce copious amounts of the neurotransmitter acetylcholine, which can also activate sweat glands served by the same nerves. Gustatory hyperhidrosis can arise from a variety of causes, including damage to or surgery on the parotid salivary gland or the nerves supplying it (supposedly the healing process winds up attaching salivary nerve endings to the sweat glands). A range of treatments is available in such cases, including injections of botulinum toxin. For ordinary gustatory sweating, just shun the jalapeños and stick to macaroni and cheese.