If you’re buying sunscreen from a Japanese brand, you’re likely to come across the PA rating system.
PA stands for protection grade of UVA system and is the Japanese measurement of sun protection, which is based on the Persistent Pigment Darkening (PPD) reaction reading at 2-4 hours of sun exposure. According to info from the wiki, the Persistent Pigment Darkening (PPD) method is a method of measuring UVA protection, similar to the SPF method of measuring UVB light protection.
These are the three levels of protection that are commonly seen:
PA+, PA++ and PA+++.
PA+ provides some UVA protection with a factor of PPD 2-4
PA++ provides moderate UVA protection with a factor of PPD 4-8
PA+++ provides good UVA protection with a factor of PPD > 8
Which means, you’re better off picking a sunscreen with PA+++ which will provide you with the greatest protection.