The cold water rinse

At the end of every shower, after I have rinsed out the conditioner, I do a thirty-second cold water rinse over my hair. The water is set to the coldest the tap will go, which in our flat is genuinely cold. The thirty seconds are uncomfortable. They are also the most reliable shine treatment I have found.

I learned this from a hairdresser in Marseille who did my hair on a holiday about six years ago. She had been a hairdresser for thirty years. She told me, while she was cutting, that the most important step in any hair-care routine was free, that most people skipped it, and that it would do more for my hair shine than any of the products she had on the shelves behind her. She was talking about the cold rinse.

Why it works

Hot water opens the hair cuticle. The cuticle is the outer layer of the hair shaft and it is made of small overlapping scales. When the cuticle is open, the hair looks dull because the light is scattering off the raised scales. When the cuticle is closed and lying flat, the hair looks shiny because the light is reflecting more uniformly off the smooth surface.

Hot water in the shower opens the cuticle, which is useful for the cleansing and the conditioning steps. The cold rinse at the end closes it again before you step out of the shower. The hair that dries with a closed cuticle is the hair that looks shiny.

What the thirty seconds feels like

Uncomfortable for the first week or two. I had to brace myself for it. By the third week the body had adapted and the thirty seconds were brief and tolerable. I look forward to them now, slightly, because the small physiological jolt is a nice way to end a shower — the body wakes up, the breath sharpens, the morning continues with a small alertness it did not have before.

The smaller payoff

There is, beyond the hair, a small mood effect from the cold rinse. The vagus nerve, which runs through the neck and which mediates a lot of the parasympathetic recovery response, is sensitive to cold water. A brief cold exposure on the head and neck has, in some studies, been associated with small mood improvements. I would not call it a treatment, but I notice that I am, slightly, calmer in the hour after a shower that ended in a cold rinse than in the hour after one that did not.

If you have been trying to find a hair shine product that works, try this first. Thirty seconds. Free. It will tell you within two weeks whether it is going to help.