Sunscreen application technique should achieve a quantity of 2 mg/cm² to all accessible skin.

The goal of a recent study published in Advances in Experimental Medicine and Biology was to investigate how the "fill up a handful of sunscreen and spread it all over your body" advice works in practice, through by quantity of sunscreen applied and amount of covered skin.

Here, 17 volunteers wearing swimwear were asked to "fill up a handful and spread it all over your body." Before and after sunscreen application, the volunteers were photographed in black light; the sunscreen container was weighed before and after to quantify the amount of sunscreen applied.

It was observed that a median of 21% of the accessible skin was left completely without coverage. While the 79% covered area had a median of 1.12 mg/cm² of sunscreen, not the expected 2 mg/cm².

The results indicated that the advice "fill up a handful of sunscreen and spread it all over your body" renders a better yet, modest protection rather than the intended effect. 

Source: Advances in Experimental Medicine and Biology. 2020;1268:381-385. doi: 10.1007/978-3-030-46227-7_19.