Hi @wormspoor,
Thanks for the question! I’d recommend that SPF and UVAPF are similar. So if a product’s SPF is 30, the UVAPF should be around 30 as well.
Why? This best mimics the reduction in UVA and UVB that shade provides.
As well this gives you a better idea of how much protection from the entire UV spectrum you’re getting. Imagine you’re using a sunscreen with SPF 50+, but only UVAPF 10. While you’re not sunburning, you’re still exposed to a good amount of UVA energy – this is why people are often confused when they develop a tan despite wearing a very high SPF.
P.S. PPD is just one of the methods used to determine UVAPF, it involves human subjects and compares how much protected vs unprotected skin darkens. Other methods involve measuring transmittance in the UVA wavelength bands.
