SPF and PFA – What do they mean?
Protection from excessive sun exposure and UV rays is one of the most basic approaches to anti-aging skin management. The importance of the use of sunscreen is well acknowledged but most people do not realize that their sunscreen does not block all UV rays well. Of the three types of UV rays (A, B, C), UV A light penetrates the deepest and induces the greatest amount of aging on the skin. Sunscreens that contain both UV A and B filters provide better protection than those with UV B filters only. Historically, most sunscreens had only UV B protection but, more recently, UV A protection is more commonplace in topical preparations. Check your sunscreen and make sure it has both.
Understanding the methods to measure sun protection is also important but poorly understood by most. The SPF system (Sun Protection factor) applies only to UV B protection. SPF 15 blocks 93%, SPF 30 97%, SPF 45 99%, so a minimum SPF would be 15. UV A light, however, is not covered by the SPF grading system. It is graded by the relatively unknown PFA system. (Protection Factor Ultraviolet A) PFA correlates well to the SPF system meaning, for example, if you normally begin to tan or burn after 20 minutes in the sun, a PFA of 15 will extend your protection 15 times longer, or 300 minutes. It is now recommended that your sunscreen have an equal proportion of SPF and PFA. Check your labels carefully.
A new UV A filter has been recently approved in 2006, Mexoryl. This has been widely used in Europe and Canada for years and we will begin seeing here in the U.S. as well now that it has been approved.
Dr Barry Eppley
Indianapolis, Indiana