《纽约时报》请皮肤科医生查证冷水洗发神话

Many people have heard that rinsing hair with cold water will make it shinier.

This claim has been around for decades and has recently been brought up repeatedly again on social media.

The reasoning sounds quite plausible: cold water can close the cuticles on the hair's surface.

Once the cuticles close, light reflects more evenly, and the hair looks shiny.

However, several dermatologists say cold water does not actually make hair shinier.

New York dermatologist Dr. Teresa Song said directly that this claim is "completely unfounded."

She said cold water probably "won't make much of a difference" to shine.

Lilia Correa Selm is an associate professor of dermatology at the University of South Florida.

She said the most suitable water temperature is lukewarm, roughly the same as body temperature.

She explained that if the water is too cold, its cleansing power decreases.

Oil, dirt, and conditioner that hasn't been rinsed out may remain on the hair.

Water that is too hot is also no good, said Jacob Beer, who works in West Palm Beach, Florida.

Hot water can dry out the scalp and even cause itching and irritation.

So where does shine actually come from?

The answer lies in the thin layer of cuticles on the surface of the hair.

Dermatologist Hope Mitchell used an analogy.

The cuticles are like overlapping shingles on a roof.

It wraps around the inside of the hair and also reflects light outward.

What we see as so-called shine is this reflection.

Fine, straight hair reflects light more evenly and looks shiny.

Thick, coarse, or curly hair scatters light, presenting a soft sheen.

So if you want shiny hair, the key is not that final blast of cold water.

Dr. Song said what really works is daily hair care habits, especially conditioner.

Beer also recommends using a silicone-based conditioner.

These products can smooth the cuticles, and shine naturally follows.

Another easily overlooked cause is friction.

Dr. Song said brushing too vigorously can damage the cuticles.

Vigorously rubbing wet hair with a towel does the same, and the hair actually becomes duller.

As for how often to wash your hair, the American Academy of Dermatology's advice depends on the individual.

People with straight hair and an oily scalp can wash once a day.

Those with dry, thick, curly, or coarse-textured hair can go two or three weeks between washes.

Many people are taken aback the first time they hear the figure of two or three weeks.

Mitchell also reminded that shiny hair does not equal healthy hair.

Some people's hair is naturally reflective.

But if the ends are split and it breaks when combed, it needs care, not more shine.

This kind of claim spreads because rinsing with cold water costs almost nothing.

And it's simple to do, and sounds harmless.

But so far, no reliable research has proven that water temperature changes hair shine.