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Did you know that temperature plays a crucial role in your wash day? After detangling and conditioning your hair under warm water, turn the dial to cold and complete your final rinse, before gently wringing the hair and styling. Cold water seals the cuticle to keep the moisture in, and makes your hair easier to finger comb during the styling process. Once it’s dry, your hair should be shinier and more defined! There are many theories about rinsing with cold water vs. hot water, so we interviewed Sister Scientist, a cosmetic chemist beauty industry expert to get the science behind using the right temperature for your natural hair.

What does hot water do to hair?

Sister Scientist: “Hot water is more effective in helping to remove dirt, oil, and build-up from the hair, but it can also remove the natural oils your hair produces to stay soft and moisturized. Use hot water in moderation.”

What’s the best temperature for washing your hair?

Sister Scientist: “Start with hot water when shampooing the hair to help open the pores on the scalp to release dirt and oil, and also enhance the studying of your shampoo. Then reduce the temperature of the water to warm on the next shampoo or rinse.”

Does cold water really seal the cuticle?

Sister Scientist: “Contrary to popular belief, there is not enough scientific evidence that supports the theory that cold water seals the hair cuticle. However, this doesn’t mean that the perceived ‘sealing’ benefits are completely false. Cold water may not physically seal the cuticle, but rather, I believe that people are observing the difference between the effects of steam and water on the hair.”

How does steam affect the hair?

Sister Scientist: “Steam often results from using hot water in small spaces (i.e. the shower”>.  The distance between water molecules that exists in a gaseous state (i.e. steam”> is much larger than the distance between liquid water molecules. Gas molecules move more freely and are highly compressible, allowing it to diffuse or penetrate the cuticle layer faster. This could give the perception that hot water opens the cuticle, and cooler water seals it.  However, all temperatures of water can penetrate and swell the hair shaft, raising the cuticle.”

What’s the best way to smooth your cuticle and prevent frizz?

Sister Scientist: “The best way to ensure the cuticle layer is nice and smooth is to make sure you use a great conditioner, no matter what the temperature of the water is.”

Now that you know the science behind hot water and cold water for your natural hair, which one will you use on your next wash day? Let us know in the comments below.

Read Next: Thicker Isn’t Always Better: Why It Doesn’t Guarantee Moisture and Slip.

This article was originally published in 2017 and has been updated.

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