Effects of solar radiation on hair and photoprotection

• Solar radiation damages hair and changes color, protein content, and resistance.
• Antioxidants, silicones, and quaternary filters are promising photoprotectors.
• There are no regulated parameters to evaluate hair products photoprotection.
• Color fading is related to the oxidation of artificial dyes and natural pheomelanin.
• White hair is more susceptible to radiation due to its low content of melanin.

In this paper the negative effects of solar radiation (ultraviolet, visible and infrared wavelengths) on hair properties like color, mechanical properties, luster, protein content, surface roughness, among others, will be discussed. Despite knowing that radiation damages hair, there are no consensus about the particular effect of each segment of solar radiation on the hair shaft. The hair photoprotection products are primarily targeted to dyed hair, specially auburn pigments, and gray shades. They are usually based on silicones, antioxidants and quaternary chemical UV filters that have more affinity for negatively charged hair surface and present higher efficacy. Unfortunately, there are no regulated parameters, like for skin photoprotection, for efficacy evaluation of hair care products, which makes impossible to compare the results published in the literature. Thus, it is important that researchers make an effort to apply experimental conditions similar to a real level of sun exposure, like dose, irradiance, time, temperature and relative humidity.