Stasya has put me on the spot.
Hi Colin, I have a question that’s been at the back my mind for some time now, and after having made my way back to your blog after some time and read your post on titanium dioxide, I figured I’d ask you. I’m sure you might agree with me that it is quite frustrating how as of date there is no universally-agreed method of categorising levels of protection against UVA radiation. I was wondering if you might be able to do a cross-comparison between the East-Asian PA (+ to +++) system based on PPD, and the Boots star rating system based on absorbance of UVA? For instance, what would PA++ be roughly equivalent to, using the Boots star rating system? Thank you for your help Stasya
Now there is a tough question! Continue reading