英语时差：嘴唇为何会干？2

What this means is that our lips have little to no protection from the environment, and their main source of moisture is the saliva that comes from our mouths. What’s more, unlike much of the rest of our body, our lips are almost always on display, and rarely covered by clothing. As a result, the moisture on our lips is continually evaporating. And that’s before we take into account exposure to sun, wind, cold, and air-conditioning. Plus, if you’re sick or have allergies, and your nose is congested, your lips end up drying more quickly because you tend to breathe through your mouth.