Ultraviolet Radiation Contributes to Hair Loss
Sunlight causes photoaging in our hair just as it ages our skin, but can it actually cause hair loss? Although hair actually serves to protect the scalp from UV radiation, research evidence suggests that it cannot completely protect the scalp and hair follicles from UV damage that may trigger or exacerbate conditions that lead to hair loss. 59, 73
Ultraviolet radiation (both UVA and UVB light) from the sun exerts a number of effects on scalp skin and hair. The most obvious effects are to the hair shaft, where UV light causes hair to lighten and become brittle. Melanin pigments (especially those in dark hair) offer some antioxidant protection against UV damage by helping prevent UV breakage of the disulfide bonds in hair protein, but as hair ages these pigments are lost. Not only does hair turn white or grey as a consequence of this, it also loses the protective benefits of melanin. 73-74
Below the surface UV radiation has mutating effects on cell DNA and induces inflammatory factors in cells. The oxidative damage caused by UV light alters the amino acids (especially tryptophan, cystine, tyrosine, and histidine) in hair shaft proteins, degrades moisturizing lipids, and breaks down the melanin pigments that help protect hair from UV light.73, 75
In addition to oxidative damage, UV also causes some immunomodulatory responses and folic acid deficiency —both of which can exacerbate conditions that are associated with hair loss, such as dermatomyositis, thyroid disorders, and lupus. 5, 73, 76 Temporary, seasonal hair loss of the telogen effluvium type may be related to UV light exposure, possibly by triggering changes in the hair growth cycle. 59 Recent studies indicate that these regular, seasonal changes in hair growth rates peaking to more than 90% of hair in anagen phase in the spring and dropping down to about 80% in late summer-autumn. 77-78
Aren't There Studies That Say UV Treatments Can Regrow Hair?
Some studies have reported that psoralen-ultraviolet A (PUVA) and UVB light can successfully regrow hair in patients with alopecia areata. 1 Psoralea is a natural source of this drug, and has been used for centuries in Traditional Chinese Medicine and kampo natural Japanese medicine to treat hair loss and inflammatory skin disorders. 79 However, retrospective analysis indicates that the overall response rate was actually much lower than reported, and perhaps not even better than if untreated and left to regrow on its own. 22 And even in those patients where UV light induced hair regrowth, the hair loss commonly reoccurs. 1
An extensive number of treatment sessions are necessary to initially achieve hair regrowth (50-80 in some studies on PUVA), and high rates of relapse indicate that even more treatments would be necessary to maintain hair regrowth. These factors suggest that these types of light therapy may not be worth the risks of UV-induced damage to the hair and scalp—including increased risk of skin cancers such as melanoma. 1, 22
However, there are some light therapies involving the use of lasers. Low level light therapy applies electromagnetic radiation emitted in wavelengths. It is non-ionizing radiation it does not have adverse effects on cells, and operates on different wavelengths than ultraviolet radiation. Studies suggest this may be an effective and safe treatment option for hair loss. 1, 80
Protection from UV-Induced Hair Damage
Hair sunscreens offer some protection from UV damage, but it is limited by two important factors, even with liberal application of the product: 74
- uneven coverage
- poor adherence to hair cuticle
And the aesthetic effect is often less than appealing, with limp and greasy hair that only makes thinning hair look worse. 74
Another way to protect hair is from the inside out:
- Hair dyes, which penetrate through to the cortex, can offer the same antioxidant protection of lost melanin pigments. Even though they may cause some initial damage to hair, experts suggest that the UV-protective benefits are worth it. 74
- Foods (e.g., coffee, tea, grains, and meats) rich in vitamin B3 (nicotinamide or niacin) may also offer protection from UV radiation DNA damage and depletion of cellular energy. Vitamin B3 is a key component of nicotinamide adenine dinucleotide (NAD)—necessary to produce cell energy and perform DNA repair. It can also be taken in supplemental form (20-500 mg/day). 49
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A systemic autoimmune disorder with various skin and muscle-related symptoms, including telogen effluvium.
A serous autoimmune disease that involves many body systems and can cause telogen effluvium or patchy alopecia areata.
Avoid sun exposure when being treated with psoralen drugs or psoralea.