Most of us don't need more than one whiff to identify that generally unpleasant, characteristic smell we call body odor.

我們多數人只需要一聞就能辨識出通常不好聞且具有個人獨特性的味道，也就是體味。

But it's a surprisingly complex phenomenon influenced by our genetic makeup, age, diet, and hygiene.

然而驚人地，體味是一個複雜的現象，受我們的基因組成、年齡、飲食和衛生習慣所影響。

So what is this odor, exactly?

所以這股味道究竟是什麼？

Where does it come from?

它從哪裡來的？

And can we do anything about it?

我們能夠改變它嗎？

To start, you just need two things to produce that familiar scent: your armpit's own secretions and the bacteria that feed on them.

首先，你只需要兩件東西就能製造這熟悉的氣味：你腋窩的分泌物和仰賴分泌物為生的細菌。

Most people associate body odor with sweat, and it's an important piece of the puzzle.

大多數人覺得體味和流汗有關，那的確是很重要的一環。

Your body has millions of sweat glands, and they come in two major types: eccrine glands are found all over your skin and secrete mainly water and salt.

你的身體有數以百萬的汗腺，他們主要能分成兩種：外分泌汗腺佈滿你所有的肌膚，主要分泌水和鹽分。

Apocrine glands, on the other hand, develop at puberty in your armpits and a few other places on your body.

另一方面，頂泌腺在青春期時開始生長在你的腋窩以及你身體的其他一些部位。

The sweat they secrete is full of proteins and fats.

他們分泌的汗富含蛋白質和脂肪。

By themselves, these secretions are usually odorless.

單單只有分泌物自己通常是沒氣味的。

That's where bacteria come in.

這也是細菌群聚的地方。

Every square centimeter of our bodies is covered with thousands of bacteria.

我們身體的每平方公分都佈滿上千隻的細菌。

Many microorganisms thrive in moist environments, like our armpits.

許多微生物在潮濕的環境下茁壯，比如我們的腋下。

There, you can find about a million bacteria per square centimeter, one of the highest concentrations anywhere on the skin.

在那裡，每平方公分可以發現上百萬的的細菌，是所有肌膚中分佈密度最高的其中一個地方。

Lurking in this throng of microorganisms are species of Corynebacteria, Staphylococci, Micrococci, and others.

潛伏在這群為生物當中的是棒狀桿菌、葡萄球菌、微球菌以及其他物種。

When these bacteria feed on the proteins and fats in apocrine sweat, they turn the odorless compounds into new ones that can smell very unpleasant.

當這些細菌以頂泌腺分泌的汗液中的蛋白質、脂肪進食時，他們將這些無味的混合物轉變成臭臭的新成分。

Some of the worst offenders may be sulfur-containing chemicals; those give body odor its oniony aroma.

其中最難聞一種大概就是含硫的化學物質，這些會讓體味有洋蔥的味道。

Carboxylic acids are in the mix, too, adding notes of cheese.

在這混合物裡同樣能找到羧酸，因而會有起司的氣味。

These molecules waft up from the armpit and can be sucked directly into our noses, where they're trapped and detected by an array of specialized receptors.

這些小分子從腋窩飄散出來，被直接吸入鼻腔中，他們滯留在那裡，被專門的感覺受器所偵測。

Those can recognize odor molecules at concentrations of less than one in a million.

即使濃度在百萬分之一以下，這些感覺受器也能感知到氣味分子。

So what determines how strong your body odor might be?

所以，什麼會影響你的體味濃度呢？

It depends on the resident microbial populations in your armpit, and the nutrients that your glands provide them with.

那取決於你腋窩下群居的微生物多寡以及你的汗腺所提供的營養。

Your genes help determine what compounds you produce, and in what quantity, so everyone has a slightly different set.

你的基因會決定你製造的混合物成分以及多寡數，所以每個人都會有些微的差異。

In fact, a gene variant that virtually eliminates body odor is common in people of East Asian descent.

事實上，一種會抑制體味的基因變體在東亞人體內很常見。

Adrenaline increases the ratio of apocrine to eccrine sweat, so body odor can be more intense when you're nervous.

腎上腺素會增加頂泌腺分泌汗液的比例，所以當你緊張時，體味會比較濃。

Bacterial composition and concentration also varies between individuals and plays a part.

細菌的組成和集中度同樣因人而異，並且也會影響體味。

Even what you eat can have a small effect on how you smell.

甚至你吃的食物也會多少影響你的體味。

So how can we deal with body odor?

那我們該如何對抗體味呢？

Washing the armpits with soap and water helps but won't remove all the bacteria since many are buried in deeper layers of the skin.

用肥皂和水清潔腋窩會有幫助，但並無法清除所有細菌，因為還有很多是深埋在皮膚底層。

Deodorants, however, inhibit bacterial activity and mask odors at the same time.

然而，體香劑能夠在抑制細菌活動的同時阻隔氣味。

Antiperspirants work by forming tiny gel plugs that block sweat glands, drying out the armpits.

止汗劑的原理則是形成微小膠塞堵住汗腺，使腋窩保持乾燥。

While we continue to battle body odor, scientists are trying to understand it.

在我們想辦法對抗體味的同時，科學家在試圖了解它。

We don't know why the brain often interprets these particular odors as off-putting .

我們不知道為什麼大腦通常將一些特定氣味解讀為噁心的。

But some researchers have proposed that secretions from the armpit could have a positive function, too, like cementing social bonds and providing a means of chemical communication.

但一些研究人員也聲稱腋窩的分泌物具有正面效用，能夠鞏固社會連結，提供一種藉由化學溝通的途徑。

We don't know yet if that's the case.

我們還不知道是不是真有這回事。

For now, body odor seems to be just another smelly part of the human condition.

現在看來，體味不過是人類發臭方面的其中一部份。