Why do white hairs turn yellow?

White hair is generally more fragile than coloured hair. This is due to the lack of melanin in the cortex of the hair fibre, the intermediate layer of the hair. Indeed, the role of melanin is not only aesthetic, it also helps to protect the hair, particularly from oxidative stress caused by UV rays or pollution. White hair being more porous, external compounds, such as chlorine from swimming pools or cigarette smoke, are more likely to deposit and remain on the fibres. These elements tend to yellow and dull the hair.

Another factor responsible for the yellowing of hair is theoxidation of melanin. This is due to oxidative stress and the presence of free radicals in the hair fibres. This oxidation results in a change in the chemical structure of melanin, leading to a yellowish colour. Although predominantly devoid of melanin, white hair fibres still contain some residues of this pigment. All hair shades can be affected by this phenomenon, but it is more visible in individuals with white hair due to colourimetric reasons. Indeed, if you add white and yellow, you get a yellowish colour, whereas if you add brown and yellow, you get more of a light chestnut.

Another cause proposed by scientists to explain the yellowing of hair is theaccumulation of kynurenine in the fibres. This pigment yellow naturally present in the body is a metabolite derived from the breakdown of tryptophan, an essential amino acid. The mechanisms explaining the degradation of tryptophan into kynurenine and the accumulation of the latter in the hair are still poorly understood to this day, but it seems that they could be influenced by genetic and environmental factors, such as sun exposure or the intake of certain medications.

Yellowing hair can give a dull appearance and sometimes be a source of insecurity. To protect your white hair from this process, there are several tips available.

• Purple or yellow-neutralising shampoos.

  Purple is the complementary colour to yellow and therefore neutralises it. The use of a purple shampoo or a yellow-neutralising shampoo, alternated with your usual care can prevent or correct yellowing. This type of shampoo is typically composed of blue or purple pigments that counterbalance the yellow colour.

• Sunscreen protection.

  The UV rays emitted by the sun are a source of oxidative stress and promote the yellowing of hair. To prevent this, we advise you to protect your scalp using a hat or a cap. You can also use a hair sun protection product. Often in the form of a spray or mist to be applied to the hair, the purpose of this type of product is to block UV rays.

• Proper hydration.

  Hydrating white hair using masks or restorative treatments helps to strengthen them and thus makes them less prone to yellowing. This type of treatment is generally applied once or twice a week to the lengths and ends of the hair, and helps to moisturise and nourish the hair.

• A swimming cap.

  If you are a swimming enthusiast, we recommend opting for a swimming cap when you go to the pool. Indeed, this will not only protect your hair from chlorine, which contributes to hair yellowing, but also prevent your lengths from tangling and damaging.

• Avoid using heating devices.

  The use of heating devices such as straightening irons or heated brushes is generally not recommended for white hair. Being highly sensitive, white hair poorly tolerates heat, which risks further weakening it and increasing its porosity. Consequently, heat indirectly promotes the deposition of external substances on the hair, leading to its yellowing.

• Avoid tobacco.

  The World Health Organisation (WHO) estimates that just over 20% of the global population smokes either occasionally or regularly. In addition to causing numerous health problems, tobacco promotes the yellowing of white hair due to the many free radicals it contains (approximately 200,000 per puff). Therefore, to limit health risks and prevent yellowing hair, it is advisable to avoid smoking.

• RAWNSLEY J. & al. Hair biology: Growth and pigmentation. Facial Plastic Surgery Clinics of North America (2018).

• PHILPOTT M. Watching hair turn grey. eLife (2021).