20 Beauty Tips Make You Look 10 Years Younger

4. Rinse Your Hair With Cold Water.

The cold water trick is based on the anatomy of the hair shaft, specifically the surrounding layer of overlapping cells called the cuticle. "The cuticle is the outermost part of the hair and resembles the shingles on a roof," Abraham Armani, M.D., a board-certified hair transplant surgeon, tells SELF. These "shingles" open and close depending on the temperature of the water you use when you wash your hair a fact you can use to your advantage.

A cool hair rinse, on the other hand, will remove excess product without stripping away all the moisturizing ingredients. (Curly-haired ladies know that more moisture equals less frizz, too.) It will also close down the cuticle cells, which has two benefits. For one, it locks those ingredients and water inside the hair strand. And when the cuticle layer is closed, the cells lay more smoothly, which makes light reflect better off the hair. More reflection equals more shine.

Washing with hot or warm water separates the overlapping cells of the cuticle, allowing the shampoo to penetrate the hair's shaft deeper. Armani says that it's the most effective way to deeply clean the hair. But the same thing that makes warm water good for washing makes it bad for conditioning.

"Using warm water can dissolve lipids and remove most of the conditioners that you added in," says Kally Papantoniou, M.D., a dermatologist with Advanced Dermatology PC, which means you can condition for 20 to 30 minutes and then immediately rinse away the nutrient-filled products, wasting time and money.