The fact that solar radiation can alter the appearance of hair is becoming more and more conscious to the mind of cosmetic consumers. In response to this, cosmetic products are tending to be more than just a concept in trying to protect the hair from those photo-induced changes.
There is also some confusion around SPF and how this translates to hair and the actual damages the rays have on our hair.
So, good to know that:
- SPF is a standard measuring factor applied to the skin ONLY. There is no Hair-SPF and the hair products that have a SPF on the package are just sending you erroneous and confusing messages.
- Some hair products show a SPF but you will see below “for scalp”; it is referring to protecting the scalp, not the hair strands.
- Effects of UVR on hair are different than those on skin.
Chronic Effects of UVR on skin and bald scalp
Terrestrial solar UVR ranges from approximately 280 to 400 nm: UVB (280-320 nm) typically induces erythema and direct DNA, whereas UVA (320-400 nm) is associated with tanning and photoaging (1). UVA also generates excess reactive oxygen species that indirectly damage DNA. (2,3). So, photocarcinogenesis and photoaging are the most two important chronic effects of UVR on the skin and bald scalp. The Sun Protection Factor (SPF) has become a worldwide standard for measuring efficacy of sunscreen products in shielding the sun’s UVR.
The SPF is defined as the ratio of the UVR dose that induces the first perceptible erythema (sunburn) on sunscreen-protected skin to the UVR dose that induces the same erythema on unprotected skin. (4).
Effects of UVR on hair fibers
Contrary to the skin, the hair will not send a message of pain because of UVR overexposure; the results are rather seen after cumulating solar radiation over several weeks.
As hair is nonliving, it cannot be sunburned or undergo photocarcinogenesis; however, UV and visible radiation are very damaging to the cosmetic value of the hair. The hair will noticeably be less manageable, weaker, more brittle and will have developed more split ends (5).
Photochemical impairment of the hair includes degradation and loss of hair proteins as well as degradation of hair pigment. UVB radiation is responsible for hair protein loss and UVA radiation is responsible for hair color changes. Moreover, a study showed that acute Telogen Effluvium (sudden increase in hair loss) from prolonged UVR exposure could occur (6).
UV exposure involves considerable changes in the structure of keratin including the photo-oxidation of amino acids, sterol and fatty acids, resulting in rupture of sulphur bridges inside the hair fiber and on the surface of the cuticle, decomposition of lipids, and degradation of the pigment (melanin).
The worst effect of sunlight on hair is cystine oxidation to cysteic acid, which modifies its mechanical properties (7,8).
The natural photoprotection in hair is melanin; the degradation of the melanin by visible and UVR in the hair shaft is called photobleaching. This phenomenon is especially pronounced in blonde hair, which lightens dramatically in the summer, but also results in permanent changes in the hair shaft internal amino acids and external lipids.
Un-pigmented hair, such as gray and white hair, is more susceptible to UV damage than pigmented hair. Also, the rate of cystine disulfide bond breakage is greater for un-pigmented than pigmented hair. This means that one of the best sources of photo-protection is hair dye.
White un-pigmented hair looses more mechanical strength after UV radiation than semi-permanently or permanent dyed brown hair. The permanent hair dye acts as a passive photo filter reducing the hair fiber protein damage by attenuating the incident light. The darker the hair color the more photo-protection imparted by the dye (9). In the same time, the hair color of the artificially dyed hair is also sensitive to sun exposure, resulting in faded and dull colors.
UV filters used in hair formulations
There are many chemicals used in hair care products in order to decrease the damage of sun exposure. They are used to protect the mechanical integrity of the hair shaft or to protect the hair color, especially for hair that has been dyed. Among these, most popular are benzophenones (for UVA-UVB), phenylbenzimidazole sulfonic acid (UV-B), butyl methoxydibenzoylmethane (UV-A), octyl dimethyl para-aminobenzoic acid PABA (UV-B).
Among these, the benzophenones have the best protection ability both on color and morphology, but there are also most unstable chemicals in formulations (10).
Most hair care products with UV filters on the market today are formulated with ethylhexyl methoxycinnamate, also called octyl methoxycinnamate or octinoxate. There are also some polymeric filters, such as the polymeric organosiloxanes, which protect the artificial hair color from fading (11).
- Divya R. Sambandan and Desiree Ratner, Sunscreens: An Overview and Update, J Am Acad Dermatol 2011;64:748-58
- Dahle J, Kvam E. Induction of delayed mutations and chromosomal instability in fibroblasts after UVA-, UVB-, and X-radiation. Cancer Res 2003; 63:1464-9.
- Marrot L, Meunier JR. Skin DNA photodamage and its biological consequences. J Am Acad Dermatol 2008; 58:S139-48.
- Reinau, U. Osterwalder, E. Stockfleth and C. Surber, Meaning and Implication of the Sun Protection Factor, British Journal of Dermatology 2005.
- Dubief, C. Experiments with hair photodegradation. Cosm.Toil.107, 95-102 (1992).
- Trüeb RM (2003) Is androgenetic alopecia a photo-aggravated dermatosis? Dermatology 207: 343-348.
- Fernández et al. / Journal of Photochemistry and Photobiology B: Biology 106 (2012) 101–106
- Habe, T., Tanji, N., Inoue, S., Okamoto, M., Tokunaga, S. and Tanamachi, H. (2011), ToF-SIMS characterization of the lipid layer on the hair surface. I: the damage caused by chemical treatments and UV radiation. Surf. Interface Anal., 43: 410–412.
- Zoe Diana Draelos, MD, Hair, sun, regulation, and beauty, Journal of Cosmetic Dermatology, 13, 1—2.
- Bernhardt et al., UV filters for hair protection, International Journal of Cosmetic Science 15,181-199 (1993).
- Maillan, UV Protection of artificially colored hair using a leve-in formulation, International Journal of Cosmetic Science, 2002, 24, 117-122.