The photolightening behaviors of red and blond hair caused by UV and visible light

What is it about?

It has been proven that chemically intact melanin in red hair is considerably more photo-labile to UV light than VIS light. Also, it is much more easily decomposed by UV light than melanin granules in blond hair, although they are both similarly decomposed by VIS light. This indicates that pheomelanin is far more sensitive to UV light than eumelanin, while these two types of melanin are similarly sensitive to VIS light.

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Why is it important?

Blond hair is lightened by visible light but is not lightened by UV light until it is washed after irradiation. On the other hand, red hair lightens to a similar extent by irradiation from both types of light. Hypothetical photolightening mechanism: When UV light is irradiated at red hair the light is absorbed by hair protein and attenuated before it reaches the melanin granules. However, since pheomelanin is highly sensitive to UV light, even the attenuated UV light decomposes the pheomelanin to some extent. As a result, UV light lightens red hair without the need for subsequent washing, which is different to blond hair that consists of mainly eumelanin.