UV damage to hair and the effect of antioxidants and metal chelators.

The micro-EPR and terephthalate fluorescent probe methods are both effective techniques to study production of free radicals by hair exposed to UV light under wet and dry conditions, respectively. Both assays are simple methods for determining the effectiveness of potential protective hair treatments against UV damage, but because they assess free radical damage under dry vs wet conditions, the chemistry created on UV exposure is different. This gives insights into mechanism of action, but results may not be consistent between the two methods for actives added for reduction of UV damage. NAC pre-treatment did reduce free radical generation in UV-exposed hair under both wet and dry conditions. Photoyellowing data are more complicated as it is a less direct measure of UV damage and is highly dependent on irradiation source. Using UVB irradiation is experimentally convenient but may not be appropriate, because UVB wavelengths comprise only 0.3% of terrestrial sunlight. The photochemistry of hair exposed to sunlight involves concurrent photobleaching and photoyellowing processes and is far more complex. Under UVB irradiation conditions, oxalic acid showed a yellowing benefit.