Behaviors like smoking and excessive alcohol consumption also have a very recognizable odor.
像抽烟和过度饮酒这样的行为也会产生一种非常明显的气味。
Regardless of cause, the bad smell almost always originates in the mouth
抛开原因不看，难闻的气味几乎总是在嘴巴里产生的，
and not the stomach or elsewhere in the body.
而不是胃或身体的其他部位。
But one of the biggest challenges lies in actually determining how our breath smells in the first place, and it's unclear why.
但是最大的挑战之一在于，真正决定我们口气是什么样的，其原因至今不明。
It may be that we're too acclimatized to the smell inside our own mouths to judge it.
也许是因为我们对自己嘴巴里的味道太过熟悉，以至于无法判断。
And methods like cupping your hands over your mouth,
像把双手合拢放在嘴前对着哈气，
or licking and smelling your wrist don't work perfectly either.
或者舔一下手腕然后闻一下味道这样的方法也不是很有效。
One study showed that even when people do this,
一项研究显示，即使在人们这么做的时候，
they tend to rate the smell subjectively according to how bad they thought it was going to be.
他们往往会根据自己觉得味道会怎么样来主观地判定口气的难闻程度。
But there's one simple, if socially difficult way of finding out how your breath smells: just take a deep breath and ask a friend.
但是有一种方法能弄明白你有没有口臭，虽然这种方法在社交上有些困难，但非常简单，那就是：深呼吸然后问问你的朋友。
