Let's start by reviewing the ways in which the surface of ourlips is different from the surface of the skin on the rest of ourbodies.
首先，我们需要知道嘴唇的表皮有别于身体其他部位的。
Basically, our lips are made of the same mucusmembrane that coats the inside of our mouths.
基本而言，嘴唇有相同的粘液膜组成，保护我们的嘴巴。
This means two things.
这就说明了两件事首先。
First, our lips don't have the same protective outer layer as the skin elsewhere on our bodies.
第一，我们身体其他部位的肌肤有一层“保护层”，这是嘴唇所没有的。
This layer is part of the barrier to evaporation, and its absence means our lip skin retains less fluid.
“保护层”能有效保湿，嘴唇因为没有而不易保湿。
Second, our lips don't have the same glands and pigments as ordinary skin.
第二，嘴唇不像其他肌肤有腺体和色素。
For example, lipsdon't have oil glands, which also help keep moisture from evaporating, and they contain lessmelanin, the pigment that helps protect our skin from sunburn.
比如，嘴唇不能分泌油脂，不易保湿。此外，嘴唇缺少黑色素等色素保护皮肤免受太阳灼伤。
What this means is that our lips have little to no protection from the environment, and their mainsource of moisture is the saliva that comes from our mouths.
这就说明嘴唇易受环境影响，而嘴唇水分大多来源于嘴里的唾液。
What's more, unlike much of therest of our body, our lips are almost always on display, and rarely covered by clothing.
此外，嘴唇有别于身体其他部位的皮肤，嘴唇经常暴露在外面。
As a result,the moisture on our lips is continually evaporating.
这样一来，嘴唇的水分一直在蒸发，
And that's before we take into account exposure to sun, wind, cold, and air-conditioning.
这还不算阳光、大风、天冷、空调的“摧残”。
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.
此外，如果你生病了或者过敏而鼻塞，不得不用嘴巴呼吸，嘴唇会干得更快！
