Now that it’s Spring (though it’s been snowing in Toronto…), I thought I would share some sunscreen tips1 to help you use it better this Spring and coming Summer!
Most people don’t apply enough sunscreen! Across multiple studies people only apply ¼ to ½ the amount needed for the protection on the sunscreen’s label. 2
You may have wondered why the US FDA and other organizations keep the amount needed for SPF testing so high, as it turns out 2.0 mg/cm2 is a bit of a sweet spot when it comes to reproducibility and reliability of the results. 3
Any easy way to help get the amount needed on the skin is to apply your sunscreen twice. Apply a layer, let it dry, then apply a second layer. This method is recommended by the Japanese Ministry of the Environment. 4
Try not to rub your sunscreen too much when you apply it, one study found that vigorous rubbing actually reduced the SPF by 25%. They think it was because the sunscreen was being rubbed off onto the hands. 5
You should wait at least 10 minutes before putting on or taking off clothes, to allow the sunscreen to dry and to prevent the clothing from wiping it off the skin. 6
The WHO recommends reapplying your sunscreen every two hours. Realistically most of us won’t do that, but you should aim to reapply your sunscreen at least once, and especially after physical activity or swimming and bathing. 7
Reapplying your sunscreen just once can reduce your risk of sunburn by 2 to 3 fold! While there’s differing advice on when to reapply, aim to do it at least once throughout the day. 8
One study found that only 60% of the applied sunscreen was still on the skin after 4 hours of wearing clothes, physical activity, and bathing, and only 40% after 8 hours. 9
If you’re on the beach, be aware that sand can remove sunscreen from the skin! Up to 59% could be potentially removed by laying on the sand. 10
Make sure to apply your sunscreen before UV exposure! One study on people on vacation found that they were, on average, getting 100 minutes of UV exposure before they applied their sunscreen! That was almost 30% of the amount needed for a sunburn in some cases. 11
While there isn’t a big difference in amount of UV filtered out by an SPF 30 and an SPF 50 sunscreen, it can help make up for us not applying enough. In an experiment, an SPF 100 sunscreen applied normally (which is to say, not enough) offered an SPF of 27. 12
…and a bonus tip! While the above animation is super-cute, it’s not super accurate. Sunscreens (both physical and chemical) don’t protect our skin by reflecting and scattering UV energy. Sunscreens attenuate the UV energy, absorbing it and turning it into less harmful energy – most often in the form of heat. Titanium dioxide and zinc oxide do reflect some of the UVA wavelengths, but they reflect much more in visible light spectrum, which is why they can leave a white-cast on the skin – micronization can help reduce this effect! 13
I hope you’ll find these tips helpful this Spring and Summer (and all-year round!), not only does reducing UV exposure slow down extrinsic ageing, hyperpigmentation of the skin, and the formation of broken capillaries, it also reduces our risk of certain types of skin cancers and helps prevent the immune suppression caused by UV – it’s win-win really!