Sunscreen Tips - Mystery of SPF
Whenever we mention SPF value, everyone seems to understand what is SPF value. But have you ever think about the true meaning of SPF? What is the actual meaning of SPF? Does a higher SPF definitely means a higher protection?
SPF (Sun Protection Factor) is currently the only factor that is nationally recognized. It is an international standard on the protection on UVB. The calculation method of SPFis very simple. Simply multiple the SPF vaule with "Skin natural self-protection time". Generally, repeated activity such as swimming, perspiring or towel drying can reduce protection time. Therefore, the maximum recommended exposure time would be 70% of the calculated protection time.
The following graphs shows the suggested protection time of SPF30 and SPF50. Generally speaking, SPF30 products can provide more than 90% protection of UVB. SPF50 can even provide more than 7 hours of protection, and is more than enough for Hong Kong people. SPF can only imply the protection value of UVB, but not for UVA and Infrared (IR-A). Therefore, higher SPF value does not mean a full spectrum protection.