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[3 min read] Sunscreen use optimised by two consecutive applications
Australians are often inadequately protected from the sun. People can become sunburned from just 10 minutes of sun exposure which heightens their risk of skin cancer and can cause irreversible damage to skin cells, resulting in skin pigmentation issues, moles and freckles, loss of skin elasticity, wrinkles and fine lines.
A study looked at how much two consecutive sunscreen applications could increase the quantity of product applied to the skin and decrease the amount of skin left unprotected compared to a single application.
Thirty-one healthy volunteers wearing swimwear were included. They applied sunscreen two consecutive times in a laboratory environment.
Participants had pictures taken in black light before and after each application. As sunscreen absorbs black light, the darkness of the skin increased with increasing amounts of sunscreen applied. Researchers conducted a standard curve establishing a link between change in picture darkness and quantity of sunscreen. The quantity of sunscreen at selected skin sites as well as the percentage of missed area was determined after each application.
Participants had missed a median of 20 per cent of their available body surface after a single application. After double application they had missed nine per cent. The decrease in missed areas was significant for the whole body surface and for each of the body regions separately. The average participant had applied between 13 and 100 per cent more sunscreen at the selected skin sites after double application than after single application.
Researchers recommended that people perform two consecutive applications of sunscreen for best coverage, especially before intense sun exposure. This recommendation is particularly prudent advice for practitioners providing skin care advice to patients looking to better maintain their skin health.
Source: Heerfordt IM, Torsnes LR, Philipsen PA, Wulf HC (2018) Sunscreen use optimized by two consecutive applications. PLoS ONE 13(3): e0193916. https://doi.org/10.1371/journal.pone.0193916
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