Hair coloring especially oxidative permanent coloring can cause some serious damage to hair during the application. However, researchers have found that coloring hair can actually protect the hair against photodamage from prolonged hours of exposure to the sun. Here we will review this underappreciated benefit of hair coloring.
Importance of melanin in hair
The pigment granules in hair (such as melanin), found in the cortex of hair, play an important role in protecting the hair from photodamage. They either absorb or scatter the light and in the process the pigments lose color as well (bleach by sunlight). For that reason, you will notice that constant exposure to sunlight can change your natural hair color to a lighter tone. In taking on the sunlight, the pigments are preventing the radiation to damage the amino acids of hair. If you remember, amino acids are the construction blocks of the hair keratin (protein fibers). Destroying or damaging them weakens the hair fiber. This fiber will have a lower mechanical strength as compared to an undamaged fiber.
Everyone has different levels of melanin or pigments in hair. The higher the level, the better the protection against sunlight. [Read more about hair damage by sunlight here.]
Hair coloring for photoprotection
In a study examining photodamage of hair over time, researchers have found that hair dyes, in general, provide protection against sun damage. This protective effect is seen even with direct or semi-permanent colors. The efficacy however is dependent on how well these semi permanent dyes deposit on hair. They compared the colored hair with undyed hair under the same experimental conditions.
Oxidation processes such as demi-permanent and permanent coloring weaken the hair initially due to chemical damage but also showed a net protection upon prolonged photo-exposure (over days). These data also reveal that the darker oxidative shades that deposit more color in hair also provide better photoprotection.
Why the dyes give protection
Dyeing of hair results in the deposition of color in the cuticles and, depending on the product, a significant amount may also penetrate all the way inside the fibers. In contrast, the natural color (melanin) is localized in the cortex. As expected the hair color partially absorbs and attenuates the incident light before it penetrates into the hair. It thus lessens the effects of sunlight on hair.
The good news: Your colored hair can help minimize photodamage, if you’ve forgotten your hat.
The caveat: In protecting the hair, the dyes will break down and cause fading, a non desirable side-effect from a cosmetic point of view.