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Sunscreen Science

By Sara Chow - June 19, 2019

You know that using sunscreen properly will prevent sunburns, skin cancer and premature aging. You also know that sunscreen is effective because every time you miss applying it in one spot there is a sunburn as evidence of your mistake. This is how sunscreen works:

The sun emits ultraviolet (UV) rays that can damage our skin, leading to sunburns, premature aging and cancer. Radiation from UV rays is broken up into three different wavelengths: UVA rays are not absorbed by the ozone and can penetrate deeply into the skin, leading to cancer and premature aging; UVB rays cause sunburns and are partially blocked by the ozone layer, and; UVC rays are absorbed by the earth’s atmosphere and are only encountered from artificial UVC radiation sources, such as tanning beds and tanning lights.

june-19-2019-sunscreen-infographic

Photo Source: American Academy of Dermatology

Sunscreen combines both organic (i.e. octyl methoxycinnamate) and inorganic ingredients (i.e. zinc or titanium oxide) to prevent UVA and UVB rays from harming our skin. The organic ingredients act as ‘sun screeners’ by absorbing UV radiation and dissipating it as heat. The inorganic ingredients act as ‘sun blockers’ by reflecting or scattering UV radiation.

The strength of sunscreen is rated by its sun protection factor (SPF), which only refers to the product’s ability to screen or block UVB rays (the ones that cause sunburns). Recently, the Canadian Cancer Society changed its recommendations from using a sunscreen with a minimum SPF of 15 to a minimum SPF of 30. A SPF 30 sunscreen will block 97% of UVB rays. Evidence suggests that there is no added benefit of using a SPF higher than 50.

It is also important to know that SPF does not refer to the amount of time you can spend outdoors before reapplying. All sunscreens should be applied to dry skin at least 15 minutes prior to sun exposure and reapplied approximately every two hours, or according to the time on the label. SPF does not measure UVA, so in order to ensure that you are protected from these harmful rays you need to purchase a product that has broad spectrum protection – both UVA and UVB protection.

All this discussion about ingredients and chemicals in sunscreen also leads to the question of whether or not it is healthy and safe to apply sunscreen on our skin? The experts say that the health benefits of using sunscreen outweigh the risks of applying these chemicals onto our skin, especially since in 2015 it was estimated that, in Canada, there would be 78,300 new cases of non-melanoma skin cancers and 6,800 Canadians diagnosed with melanoma.

When you purchase sunscreen, look for a product that has a SPF of at least 30, broad spectrum protection against both UVA and UVB rays, and, as an added bonus, is water resistant.  Finally, remember that the science behind sunscreen is only useful and effective when you wear it and reapply.

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