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If you got to spend time with your family back during the holidays, you might have noticed that grandpa smells a little… old.
如果你的假期和家人待在一起，你可能会注意到爷爷笑起来有点...老。
Not stinky or bad — he just had that distinctive old person smell which some people describe as grassy or greasy.
这样并不恶心也不糟糕—只是那种笑是典型的老年人式微笑，有些人将其描述为油脂过多的微笑。
And you weren’t imagining it, either.
你也绝对想象不到。
Like baby humans, older humans do have a certain odor, and it’s likely caused by the chemical nonenal.
就像是人类婴儿、老年人都会带有某种气味，这似乎是由化学壬烯醛所引起的。
More specifically, that smell is caused by a version of the molecule called 2-nonenal, and it occurs naturally on human skin.
具体来说，这种气味是由被称为2-壬烯醛的分子的一种版本所引起的，通常反应于人类皮肤上。
Researchers have found that nonenal begins appearing around age 40, and that the amount of it increases as you age.
研究员发现壬烯醛在约40岁时出现，并随着年龄的增长而增加。
It all has to do with the complex chemistry in your skin.
这一切都与皮肤中复杂的化学物有关。
See, your skin secrets fats to help form a barrier between your body and everything in the outside world.
你看，皮肤藏着的油脂能够帮助在你身体和外界物质之间形成屏障。
It helps keep moisture in and bad things out. And these fats are found in the outer layer of your skin — the stratum corneum.
它能帮助锁住水分并排除有害物质。这些油脂位于你皮肤的外层—角质层。
Now, when those fats are exposed to oxygen in air, they start to break down and form other chemicals, also known as being oxidized.
现在当那些油脂暴露于空气中的氧气之中，就会开始分解并形成其他化学物质，同样也称为被氧化。
But your body kind of needs those fats. So to help prevent this, your skin also produces antioxidants.
但你的身体又需要那些油脂。所以为了预防流失，你的皮肤也同样产生抗氧化剂。
But as you age, two things happen. One is that your skin produces fewer antioxidants, so more fats get oxidized.
但随着年龄增长，会发生两件事。第一是你的皮肤产生越来越少的抗氧化剂，因此更多油脂会被氧化。
And the other is that the types of fats your skin secretes also changes, which might have to do with how your hormones change over time.
另一件事是你皮肤所藏匿的油脂类型同样改变了，这或许和你的激素变化有关。
And when those new fats get oxidized, that creates nonenal. As you get older, your skin produces more of these specific fats and fewer antioxidants.
当那些新油脂被氧化时，就会产生壬烯醛。随着年龄增长，你的皮肤产生更多那种特别油脂以及更少的抗氧化剂。
So you get more nonenal, and more Old People Smell.
所以你会获得更多的壬烯醛以及更多的老年人气味。
So what can you do about it? Not much. Nonenal isn't water-soluble, which means it won't dissolve in water and it's hard to wash off.
那么我们能做些什么呢？能做的不多。壬烯醛不是可溶于水的，这就意味着它无法在水中溶解，很难清洗掉。
Soap can remove non-water soluble substances, but it doesn't remove all the fats from your skin.
肥皂能够洗掉非水溶性物质，但却不能洗掉你皮肤上的所有油脂。
If it did, your skin would be really dry and uncomfortable. Which means that, even after bathing, some nonenal is still left on your body.
如果洗掉，你的皮肤会变得非常干燥且不适。这就意味着，即使在洗完澡之后，仍有些壬烯醛会留在你的身体上。
And while many commercial soaps contain deodorants to combat other bodily odors, most don't yet contain deodorants targeted for nonenal.
虽然许多售卖的肥皂都含有香体剂能够消除身体的体味，但多数肥皂却不含有对抗壬烯醛的香体剂。
So smelling like it does not indicate poor hygiene.
所以闻起来臭臭的并不代表卫生情况糟糕。
Whether or not you like the smell probably depends on your personal experiences, your culture, and how you feel about getting older,
你是否喜欢这种气味取决于你的个人经历、文化以及你如何看待衰老，
but by itself, that smell is a totally normal part of aging.
但是就其本身而言，那种气味完全是老年化的正常部分。
In fact, in a blind sniff test, the body odor of people over age 75 was described as "neutral" and rated as less unpleasant than that of young or middle-aged people.
事实上，在一场盲嗅测试中，75岁以上老年人的体味被描述为“中性味道”并被认为比少年或中年人的味道要好些。
And in general, you might even consider nonenal as the smell of a survivor, of experience...or of the most interesting people in the world.
通常你或许甚至将这种壬烯醛认为是幸存者、经历或者是世界上最有趣的人的味道。
Thanks for asking, and thanks to all of our awesome patrons on Patreon who keep these answers coming.
感谢提问，感谢所有Patreon上一直提问的赞助人。
If you'd like to submit a question to be answered, you can go to patreon.com/scishow.
如果想要提问，请登录patreon.com/scishow。
