Every time I go into a salon I overhear hairstylists giving their clients pep talks. I'm not talking about the "Oh, girl, you're too good for him" stuff you hear in movies. I hear them coaxing, plying, persuading women to do something they're afraid to do to their hair: Rinse it under cold water. The idea is that the frigid temperatures will leave your hair looking extra shiny, and most women suck it up and lean back into the chilly stream in the name of beauty. But as I sit there watching, I can't help but question if it's even working. I've tried the beauty hack a few times, but I've never been able to tell if the icy wash really made any difference. So I decided to go to the pros to find out if there's any scientific reason that we should be braving cold rinses.
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.
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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.
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.
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Not everyone is convinced the method shows results when it comes to shine, though. Philip Kingsley trichologist Anabel Kingsley tells SELF, "Unless you like the sensation of cold water, there are no benefits to it," and warns that freezing water can constrict capillaries in the scalp, temporarily decreasing blood supply. If you're sensitive, keep the water cool, not painfully cold, and aim the spray toward the mid-lengths to spare your scalp. You might notice a boost in shine—and if not, at least you didn’t wash away all that expensive conditioner.
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