Guide
What do SPF, broad spectrum and PA on a sunscreen label tell me?
SPF is built on sunburn, so it mostly describes protection from UVB rays. UVA protection is shown separately: as broad spectrum on US labels and as a PA grade on Korean ones.
What the SPF number measures
SPF compares how much UV it takes to barely redden skin with the sunscreen on versus without it, tested with a generous layer. Because sunburn comes mainly from UVB, the number speaks mostly to UVB. The US FDA also points out that SPF is not a timer: it does not tell you how many hours you can stay outside.
Where UVA shows up on the label
In the US, broad spectrum is an optional claim a sunscreen can make only after passing an FDA test for UVA protection as well as UVB. Not every sunscreen qualifies, and those that do not must say they only help prevent sunburn. Korean sunscreens report a PA grade next to SPF as their UVA measure. Other regions use their own marks, and the methods are not interchangeable.
Every number assumes enough product
Labelled figures are measured with a thick, even layer, and many people use less, so real protection can fall short of the label. DermNet describes SPF 30 and up as high protection and 50 and up as very high, when enough is applied. The US FDA recommends broad spectrum with SPF 15 or more; the American Academy of Dermatology advises SPF 30 or more.
Try this
- Look for an SPF number and a UVA mark together.
- On Korean labels, find the PA grade beside the SPF.
- Apply a full, even layer so the label figure holds.
A common mistake
Reading a high SPF as complete UVA coverage, when UVA is rated by a separate mark such as broad spectrum or PA.