What's all this stuff about PPD and why should I give a damn?

So you know when you're going on holiday, or you're going out for a day in the sunshine and you pick up your bottle of suntan lotion, do you ever think about that all those bits of information on the bottle really mean? I mean SPF 50 is high and SPF 8 is low right? That's about the majority of my knowledge on this subject a year ago. Yes I wore suntan lotion if I went on holiday or if I was going to be outside in the sun for a long time but that's it. Then I started getting more into skincare and discovered that wearing a dedicated sunscreen in really the best thing you can do for your skin. Everyone knows how damaging the sun can be. But it turns out we don't just need to worry about burning, we need to worry about the constant exposure too.

So, you may have heard of UVB and UVA rays. In basic terms, UVB rays cause burning and UVA causes aging (that's not what it stands for, it's just a handy way to remember it). When the SPF rating was first devised, it focus solely on the protection from UVB rays, as the main culprit of sunburns and skin cancer. Over time though, there was more information on the damage that UVA rays also cause and in 2007 the FDA proposed an improvement on the testing methods and labeling of UVA protection on sunscreens.

 So where are we at with this? Really, the system still isn't as transparent as it should be.  There are a few different ways that UVA protection are displayed, which really means that if you want to be diligent about sun protection, you kind of have to know about all of them.

PPD

First there is the PPD which stands for persistent pigment darkening. The PPD method uses UVA radiation to cause a persistent darkening or tanning of the skin. Theoretically, a sunscreen with a PPD rating of 10 should allow a person 10 times as much UVA exposure as would be without protection. This is a good rating to go by, as there is a lot more transparency in the numbers. The other two main rating methods for UVA protection are only split into a small number of categories, whereas with the PPD rating you can figure out if the PPD level is, for example, 4 or 40.

PA rating

The PA rating is the Japanese standard UVA protection rating. The protection is marked by plus symbols, so you can get PA+, PA++, PA+++ and the highest rating PA++++.

PA+ = 2-4PPD
PA++ = 4-8PPD
PA+++ = 8-16PPD
PA++++ = 16 and over

The problem with this method is that once you are into the PA++++ category you have no way of knowing how high the PPD level is. You could be getting the 16, you could be getting much much higher.

The Boots/Diffey star rating

Based on original work by Prof. Brian Diffey at Newcastle University, the Boots Company in Nottingham, UK, developed the star rating, which has been adopted by most sunscreens manufactured in the UK. As you can see, it works similarly in the way that the Japanese rating system does, by splitting the protection factors into smaller groups.

All in all, it can get pretty confusing trying to break down all of these numbers and symbols. If you take one thing away from this post, make it that you need a broadspectrum sunscreen, something that will protect you from both UVB and UVA rays. If you take two things from this post, make the second one that the higher the number, the higher the pluses or the higher the stars, the better.