How Does Solar UV Radiation Impact Hair Health?
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As summer comes, the days are much longer, making it a great time to enjoy outdoor activities. We all tend to linger outside under warm sunshine. But while you’re taking full advantage of summer – beach walk, outdoor sports, or sunbathing – we’re afraid those bright sunny days don’t always equal happiness to your hair. When you have fun under the sun and benefit from the sunshine vitamin (a.k.a, vitamin D), you may risk your hair being damaged significantly by ultraviolet (UV) radiation.

For your thorough understanding of the impacts of UV radiation on hair health together with solutions to limit possible damages, we have rounded up everything you need to know here in this article.

 

What is UV radiation?

Solar ultraviolet (UV) radiation is a form of non-ionizing radiation, low-energy electromagnetic waves incapable of producing ions while passing through matters. It incorporates three groups of rays based on the measure of their wavelength in nanometers:

  • Longwave UVA: 320 – 400 nm
  • Mediumwave UVB: 290 – 320 nm
  • Shortwave UVC: 100 - 290 nm

The sources of UV radiation can be either natural (i.e., the sun) or artificial (e.g., tanning beds, fluorescent and incandescent lights, lasers). Due to its short length, all the UVC and most of the UVB radiation coming from the sun are absorbed by the ozone layer before they could reach the ground. Meanwhile, nearly all UVA radiation goes further and hits the earth’s surface.

UV radiation levels can differ depending on various factors, such as sun elevation, latitude, cloud cover, altitude, ozone, ground reflection, and seasons. Different surfaces reflect or scatter different extents of UV radiation. For example, the UV radiation levels are higher in tropical regions than the temperate zones. Fresh snow, dry beach sand, and sea foam reflect around 80%, 15%, and 25% of UV radiation, respectively. Unsurprisingly, shade can reduce UV radiation by 50% or more, thus, the amount of yearly UV exposure indoor workers receive is only around 10% to 20% of outdoor workers.

It is noticeable that during midday in the summer months, the sun’s UV radiation is at its highest.

Benefits of UV radiation

UV radiation has many positive impacts on skin and hair. However, to harness UV radiation, its levels need to be observed and controlled in many cases.

One widely-known benefit of UV radiation is its influence on the vitamin D levels in your body, which positively impacts hair growth. Research has found that a majority of your vitamin-D requirement is formed within the skin through the action of sunlight. Notably, you only need around 5 to 10 minutes, a few days per week to get enough sunlight to reap the health benefits. 

Moreover, acne and fungal infections of the skin and scalp can be treated well by controlled UV exposure. Skin disorders such as eczema and psoriasis may be improved by phototherapy using a machine to create certain forms of UV radiation. For example, UVB is often used as a medical treatment for most psoriasis patients since it can slow down the abnormal growth of skin cells.

 

How does solar UV radiation damage your hair?

Along with its benefits, UV radiation, especially solar UV radiation, does hold potentially serious risks for the scalp and hair. As the scalp is the highest part of the human body, by default, it is the part that gets exposed to sunlight the most. Therefore, this area has a high incidence of precancerous lesions and skin cancers. However, thanks to the protection from hair, melanoma, a form of skin cancer, is less common in your head and neck compared with other bare areas of your body.

With that said, to protect the scalp from UV radiation, your hair has to confront all damages that UV radiation can cause.

 

Increasing dehydration and permeability of the hair

It is well known that UV radiation can cause hair damages such as loss of tensile strength and shine, embrittlement, split ends, and hair friction. These damages are induced by the decrease of hydration and the increase of permeability of your hair as a result of prolonged exposure to sunlight. During such exposure, noticeable shifts of the keratin structure in your hair can occur, including the amino acid, sterol, and fatty acid reactions. Therefore, severe disturbance among sulfur bridges, lipid decomposition, melanin reduction as well as countless micro-molecular destruction may arise, devastating hair strands from the core.

 

Bleaching and degrading hair properties

Moreover, UV radiation could even degrade and bleach your hair due to the oxidation of melanin. For example, blond hair becomes lightened, while red, and brown ones can shift to an orange tone. Because UV rays can provoke free radicals in hair structure, they destroy hair melanin and dissolve vital components for hair growth (i.e., amino acids, peptides, proteins). That, in turn, results in modifications of hair mechanical properties and eventually alter your hair well-being and color. Especially for chemical-treated hair (e.g., dyed or chemically straightened hair), the process of degradation and bleaching generated by sunlight occurs more seriously.

 

Damages to hair follicles

Hair follicles may also be damaged critically as a consequence of extended UV exposure, which could take place in several different forms. One of the recognised damages from UV radiation is hair follicle dystrophy, where UV radiation alters DNA in hair follicle tissue, leading to increased fragility of the shaft.

Furthermore, under a high dose of UV radiation, hair follicles tend to suffer from the inhibition of keratinocyte proliferation and increasing quantity of dead cells. It will cause premature catagen development, which means a shortened anagen phase.

And the final acute response of hair follicles to UV radiation is the elimination of perifollicular mast cells. Mast cells are important in regulating hair growth, maintaining follicle immune privilege, and supporting the process of follicle responses to oxidative damage. Research has found that UV radiation causes granule loss of mast cells, thus inhibiting their activities. Consequently, hair growth will be impeded.

 

Adapted from “Transepidermal UV radiation of scalp skin ex vivo induces hair follicle damage that is alleviated by the topical treatment with caffeine”, by Gherardini et al., 2019, Int. Journal of Cosmetic Science, 41(2), 164-182
 

Protect your hair from UV radiation during summer

Even though UV radiation poses many threats to the integrity of your hair, there are effective ways you can do to prevent the harm of UV radiation while enjoying abundant benefits from it. 

First, drinking enough water is a fundamental way to maintain the moisture of the whole body as well as your scalp and hair throughout heating summer days. When your body lacks water, hair follicles become dehydrated, weak, and more vulnerable to the influence of UV radiation.

After being dehydrated, the moisture level of your hair might not be able to restore as before. To prevent such dehydration, you can coat your hair with a leave-in conditioner before going out under the sun to adequately supply it with moisture.

Another way to provide enough moisture for your hair in the summertime is to use proper shampoo and conditioner that could clean your scalp while hydrating hair effectively. Remember to apply shampoo to the scalp only and the conditioner to the lengths only.

Lastly, as sunlight exposure is harmful to hair color, you might want to consider using hair sunscreen and a hat every time you get outside under the sun. Besides hats, ladies, you could braid your hair instead of arranging it into a ponytail. That would limit the extent of hair exposed to sunlight.

 

Conclusion

We usually try to protect our skin from sunlight more so than our hair. However, the damage that UV radiation can cause to hair health is noticeable. Your hair can negatively alter shine and color with split ends, and end up looking lacklustre. Moreover, sunlight induces the decomposition of hair peptides and lipids, leaving your hair weak, dehydrated, frizzy, and breakable.

As the intensity of UV radiation is highest in the summertime, it is essential to protect, nurture, and moisture your hair profusely. Avoid chemical hair treatments such as bleaching, dyeing, or straightening as much as you can since these processes modify your hair structure and make your hair more vulnerable.

 

 

References

Fernández, E., Barba, C., Alonso, C., Martí, M., Parra, J. L., & Coderch, L. (2012). Photodamage determination of human hair. Journal of Photochemistry and Photobiology B: Biology, 106, 101–106. https://doi.org/10.1016/j.jphotobiol.2011.10.011

Gherardini, J., Wegner, J., Chéret, J., Ghatak, S., Lehmann, J., Alam, M., Jimenez, F., Funk, W., Böhm, M., Botchkareva, N. V., Ward, C., Paus, R., & Bertolini, M. (2019). Transepidermal UV radiation of scalp skin ex vivo induces hair follicle damage that is alleviated by the topical treatment with caffeine. International Journal of Cosmetic Science, 41(2), 164–182. https://doi.org/10.1111/ics.12521

Millington, K. R., & Marsh, J. M. (2020). UV damage to hair and the effect of antioxidants and metal chelators. International Journal of Cosmetic Science, 42(2), 174–184. https://doi.org/10.1111/ics.12601

Rafieepour, A., Ghamari, F., Mohammadbeigi, A., & Asghari, M. (2015). Seasonal Variation in Exposure Level of Types A and B Ultraviolet Radiation: An Environmental Skin Carcinogen. Annals of Medical and Health Sciences Research, 5(2), 129–133. https://doi.org/10.4103/2141-9248.153623

Robbins, C. R. (2012). Chemical and Physical Behavior of Human Hair (5th ed. 2012.). Springer Berlin Heidelberg. https://doi.org/10.1007/978-3-642-25611-0

https://www.cdc.gov/nceh/features/uv-radiation-safety/index.html