Science-y Hair Blog © 2011 by Wendy M.S. is licensed under CC BY-NC-ND 4.0 
How much UV light from the sun does your hair filter out? It's really variable from person to person and depends on a number of conditions! If you rely on your hair to protect your scalp in the sun - read on.
Whether you are an outdoors worker, do outdoor sports, gardening, hiking, or just relaxing, you need information to make good decisions about scalp protection in the sun.
Your scalp - especially the top is always facing the sun. Especially during the strongest rays of the day.
Skin cancer: People with very light skin (Fitzpatrick Phototype 1, 2) are at highest risk of melanoma and non-melanoma skin cancer from that sun exposure. People with deeper skin tones (i.e. Fitzpatrick Phototype 3 and higher) may be susceptible to hyperpigmentation with UV exposure. While people with deeper skin tones have an overall lower risk of skin cancer, they have an increased risk of dying of skin cancer due to delays in identification and treatment.
Skin aging: All of us are at risk of skin dehydration, irritation, and worsening of pre-existing scalp conditions with UV exposure. UV-induced signs of skin aging like uneven skin tone happen to all of us - think of sun-spots on your scalp and in your hairline.
Hair loss: Chronic UV exposure can contribute to the inflammation and oxidative stress that is part of the process of thinning hair / pattern hair loss, so even if you don’t worry about skin cancer, a UV-exposed scalp might be bad news for hair-density in the long run.
> When one group of researchers applied hair of different lengths and densities to a mannequin and turned on the artificial UV light, they achieved a UPF of 5 to 15 from the hair. This study had outdoor workers in mind, people who have high exposure and traditionally (in the US) low compliance with hat-wearing.
> Another group of researchers used a mathematical and physical modeling system designed to estimate UV exposure on different parts of the body, and then engineered that model to estimate the effect of 2 different hair densities to and shapes to estimate protection by hairs, resulting in an estimated UPF of 30-65 for hair of different orientation and color. They believed the lab-derived estimates were too low.
> Yet another group of researchers used hairs of similar width, but different colors (brown, red, blonde, white), with artificial UV light directed through the hair alone (not on a 3-dimensional surface), found a UPF from 10-40+, depending on hair color and hair density.
This table summarizes the results for only the measurement-derived results. Why does it say "UPF 0-10" - I'm reminding you about your part. It gets zero protection. The color-blocks show you which hair-colors performed at these UPF ratings. White/silver hair has less pigment and can only achieve UPF of 20 with High Density. Colors shown are: Blonde, silver (gray), brown, red, dark brown/black, white.
Background Info:
- SPF is the way sunscreens are measured in the US, it accounts for UVB ray-protection only. UVB rays cause burning, and can contribute to skin cancer.
- If you have an SPF of 50, then 1/50 of the UVB rays are getting through the correct dose of sunscreen.
- UPF is the measurement used for clothing, and includes both UVA and UVB.
- If “UPF 50,” is indicated, then 1/50 of the UV rays can get through. UPF includes more of the UV rays that can damage your skin.
- Average hair density per square cm is around 150-200 depending on age, ethnicity, and normal variation between individuals.
- Extremely dense hair can be 500 hairs per square cm or greater. If you have lots and lots of hair and can barely see scalp in your part, this might be you.
- Orientation of hair: Parallel hairs provided better protection than randomly aligned hairs in the model, possibly because they provided a cumulative effect that is lost when hairs are aligned less evenly.
- Prove it: If you have long-enough hair - pull it in front of your eyes facing a bright light while loose. Then pull the hairs straight and neat (and perhaps more compact unless your hair is straight). You can see less light under the latter conditions.
- Hair color: Darker colors absorb more UV than lighter colors. This is true for clothing too. The molecular structure of darker pigments absorb light in the UV spectrum.
- If you are an outdoor worker, or spend extended time in the sun, your hair is not enough to protect your scalp unless it is very thick, or piled thickly on top of your head.
- Remember - UPF of 10 for average-density hair is nice, but we can do better.
- Hair-partings need protection on everybody. Dab on sunscreen if you can't wear a head-cover.
- Hats that are listed as UPF 30 or UPF 50 provide good protection for scalp - and help the eyes and tops of ears.
- Hats or head-coverings that are not UPF-listed will work better if they have: Darker colors, tighter weave (less light gets through), or more than one layer.
Birnbaum MR, McLellan BN, Shapiro J, Ye K, Reid SD. Evaluation of Hair Density in Different Ethnicities in a Healthy American Population Using Quantitative Trichoscopic Analysis. Skin Appendage Disord. 2018 Oct;4(4):304-307
Fijałkowska M, Koziej M, Antoszewski B. Detailed head localization and incidence of skin cancers. Sci Rep. 2021 Jun 11;11(1):12391. doi: 10.1038/s41598-021-91942-5.
Gherardini J, Wegner J, Chéret J, Ghatak S, Lehmann J, Alam M, Jimenez F, Funk W, Böhm M, Botchkareva NV, Ward C, Paus R, Bertolini M. Transepidermal UV radiation of scalp skin ex vivo induces hair follicle damage that is alleviated by the topical treatment with caffeine. Int J Cosmet Sci. 2019 Apr;41(2):164-182. doi: 10.1111/ics.12521.
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