Even if you're using SPF50+ sunscreen every day, there's a good chance you aren't properly protected by sunscreen.
A study examined the results when people applied a single full-body coating of sunscreen. After application, subjects were photographed with a UV light that showed which areas of the body were adequately covered by sunscreen.
Unsurprisingly, people are much better at applying sunscreen on the front half of the body. On average, 4.4 percent of the front side was not covered adequately by sunscreen, whereas 17.3 per cent of the back side was not covered. Men and women achieved similar results.
On the back side, women performed significantly better than men, leaving 13.6 per cent of the back uncovered. Men failed to cover 21.9 per cent of their back side.
The study shows that we need to be careful when applying sunscreen. If possible, have someone help you apply sunscreen to your back. If you can't do this, it might be safer to wear a T-shirt or rash vest at all times when you are outside. Also, remember to reapply your sunscreen — it might help you cover areas you missed on your first application.
Jovanovic, Z. , Schornstein, T. , Sutor, A. , Neufang, G. and Hagens, R. (2017), Conventional sunscreen application does not lead to sufficient body coverage. Int J Cosmet Sci, 39: 550-555. https://doi.org/10.1111/ics.12413