Why Gray Hair Turns Yellow and What You Can Do About It

Research links the yellow in gray hair to the breakdown of tryptophan, one of the building blocks of hair protein, into yellow compounds. White hair has no melanin to hide the change, so it shows. Heat makes white hair yellower in lab tests, and tobacco smoke can stain it too. Lower heat, a trim and an occasional toning shampoo are the practical answers.

This post is part of our guide to caring for gray hair. Here is what the research found, in plain terms.

What the yellow is made of

A 2009 study in the International Journal of Cosmetic Science looked closely at gray hair from 11 people. The researchers separated the white hairs from the pigmented ones. Then they measured how yellow each sample was and how strongly it gave off light when lit with ultraviolet light. That second test helps show which compounds are in the hair.

The pattern was clear. The more yellow a white hair was, the stronger the signal from compounds that form when tryptophan breaks down, compared with tryptophan itself. These compounds belong to a family called kynurenines. Yellow white hair showed a build-up of one of them, 3-hydroxykynurenine.

The study also looked along the length of each hair. Tryptophan broke down over time, faster in white hairs than in pigmented ones, and the yellow grew stronger toward the ends. The ends are the oldest part of a hair, so older hair was yellower.

Why is this so visible in gray hair? A 2014 study in the Journal of Photochemistry and Photobiology B states the reason simply: white hair has no melanin, so the effects of this kind of damage are more visible. The same study adds that the exact origin of yellowing is still not fully established.

Heat is the clearest trigger

Of the factors tested in these studies, heat gave the most consistent result. In the 2014 study, researchers heated gray hair to 81 °C, and its white hairs became yellower. A 2015 review in the International Journal of Trichology explains the chemistry: heat breaks tryptophan down into kynurenine-type compounds, and the result is yellowing of white hair.

That makes hot tools the first thing to look at. The American Academy of Dermatology (AAD) suggests:

• Letting hair air dry when possible.
• Using the lowest heat setting.
• Limiting the time a curling iron or hot comb touches your hair.
• Using these tools once a week or less.

Our page on styling gray hair has more on getting a good result with less heat.

The sun: a mixed picture

White hair is commonly said to turn yellower in the sun, as the authors of a 2007 study in the same journal point out. Their lab results were less simple. When they exposed white hair to lamp light, light that included ultraviolet made it less yellow. Only infrared light made it yellower. The 2014 study found that light could either yellow or bleach white hair, depending on the type of light and how yellow the hair was at the start.

Still, real hair spends months in daylight, and the 2009 study saw tryptophan break down along the hair as it aged. Sun also does other harm. In an AAD article, dermatologist Farah Moustafa says gray hair is more susceptible to sun damage than darker shades because it lacks melanin, and that UV damage breaks down hair proteins and changes hair color. So a hat in strong sun is worth it for several reasons. Our page on gray hair and sun covers the options.

Other causes

• Tobacco smoke. A 2021 review in the journal Cureus describes yellow staining of white mustache hair in people who had smoked for years.
• Medicines and health. The same review lists environmental and work exposures, some medicines and certain nutrition problems, such as vitamin B12 deficiency, among known causes of yellow hair.
• Hard water. We found no good study showing that it yellows hair. A 2013 study in the International Journal of Trichology soaked hair samples in hard water every other day for 30 days and found no difference in strength or stretch compared with distilled water. It did not measure color.

What helps

1. Turn the heat down. Of all the causes above, this one has the clearest evidence and is the easiest to control.
2. Trim the ends. The yellow is strongest in the oldest part of the hair, which is what a trim removes. In a Cleveland Clinic article, dermatologist Wilma Bergfeld also says regular trims keep hair from breaking.
3. Use a toning shampoo if you want to. Purple sits opposite yellow on the color wheel, so a faint violet tint cancels part of a yellow cast, as a Healthline article explains. Many are meant for once or twice a week, and overuse can leave a purple, pink or blue tint. Toning hides the yellow. The breakdown compounds stay in the hair.
4. Wear a hat in strong sun, and avoid peak hours from 10 a.m. to 2 p.m., as the AAD suggests.
5. Keep hair away from smoke.

Our page on yellowing and purple shampoo explains how to use toning products without overdoing it.

When to see a doctor

A yellow cast on gray hair is common, as the 2014 study notes. But if your hair changes color quickly, or the change comes with other symptoms, see a doctor. The 2021 review is a reminder that yellow hair is sometimes linked to medicines or nutrition problems. This post is general information, not medical advice.

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