5 Things You Should Never Do With Wet Hair (We're Guilty Of No. 1) You could say that when it comes to most matters of our health, hydration is the name of the game. Drinking water is pretty much Rule No. 1 to help our bodies function at their best. Moisturizing our faces is an unskippable part of our daily skin care routine. Our hair, on the other hand, is a different story. Listen up: Wet hair is weak hair. If there's one thing you should always remember about healthy hair care, it's this: Hair is most vulnerable to damage when it's wet.Our hair is made up mostly of proteins called keratin, which are protected by a thin, scale-like outer layer called the cuticle. Think of the cuticle as flexible shingles on a roof: The moment you wet your hair, water gets in between the gaps and absorbed into the cortex, causing the strand to swell up.And as it swells and stretches, the cuticle deforms—its edges lift up and crack. "Hair is very elastic when it's wet," explains Clay Nielsen, a hair care expert and celebrity stylist, "so when it dries, it's prone to breakage as it shrinks."The cuticle can stay lifted and cracked, even as the strand relaxes, giving our hair that rough and damaged feeling. No thanks! Below, read on for five things that you really don't want to do while your hair is in its most fragile state—and what to do instead to protect it from further damage. What NOT to do when your hair is wet.