Gray hair has a higher susceptibility to damage when exposed to UVA and UVB radiation.
Those with a significant amount of gray hair are keenly aware that it behaves differently than the rest of their tresses. By definition, gray hair is lacking color, leading to less luster and shine. It often doesn't have the same curl pattern or texture as the rest of the hair, which can make it appear unruly. Gray hair may also seem drier and more prone to frizz. However, really well-kept gray hair can be quite attractive. It is very delicate, though, and is especially prone to photo degradation and yellowing when exposed to excessive amounts of sunlight. This tendency is of particular concern as spring approaches, and many plan to spend more time outdoors gardening, swimming, or just basking in the sunshine. Fortunately, being armed with knowledge of the unique risks of sun exposure to gray hair can make it possible to prevent damage and maintain a healthy head of hair. So what does science tell us about gray hair and ultraviolet rays?
Testing and Data
Researchers have done comparative studies on various physical and chemical properties of blonde, brown, and gray hair, both before and after UV irradiation. One notable study examined a wide array of properties, including tensile modulus, tensile strength, wet combing forces, degree of swelling in basic solution, cuticle abrasion, and dynamic contact angle. They also assessed changes in hair color with exposure to UV radiation. All of these properties provided them with indirect information about the biopolymeric structure of the hair strands and how they were affected by the experimental conditions.
What they found was that the gray hair had a much higher susceptibility to damage than did the brown hair when exposed to both UVA and UVB radiation. The samples had a higher loss of mechanical strength, greater color change (yellowing), increased cuticle damage, and exhibited a marked transition from being hydrophobic to hydrophilic at the surface of the hair strands. This meant the gray hair was more likely to exhibit signs of yellowing after exposure, to become more easily tangled, to lose moisture easily, and to break. It was evident to this group that gray hair requires protection if it is going to be in the sun for prolonged periods.
For this reason, these researchers also performed their study using two different UV absorbers that have been used successfully in skin care products. One was octyl methoxy cinnamate (OMC), a commonly utilized sunscreen additive, frequently found in hair care products marketed as being effective for color retention and sun protection. The other ingredient was cinnamidopropyltrimonium chloride (CATC), a quaternized (cationic) UV absorber. Each UV absorber was applied to the hair via a soak/rinse cycle in a simple shampoo-like solution of SLS/sunscreen. The samples were irradiated for specified periods of time and then run through all of the same testing as the ones previously discussed.