THE SCIENCE OF SUNSCREEN
The sun’s out, and in true South African style we’ll be beaching and braaing our way through the holidays. By now everyone knows the dangers of sun damage to your skin and that you should be wearing sunscreen at all times, but are you using it correctly? How does sunscreen actually work?
WHAT’S IN THEM?
Sunscreens work in a few different ways. They usually contain inorganic chemicals like zinc oxide or titanium dioxide, which actually reflect UV rays away from your skin. Remember the thick, white, paint-like sunscreen noses people sported in the 80s and early 90s? They were slathered in those inorganic compounds. Nowadays, the particles of these compounds are much smaller and practically invisible. Sunscreens also often contain organic chemicals, like avobenzone or oxybenzone. Rather than deflecting the UV light, the molecules absorb the UV radiation through their chemical bonds. As the bonds absorb the radiation, the components of the sunscreen break down and release heat.
WHAT IS SPF, REALLY?
SPF stands for sun protection factor, and refers to how well the sunscreen protects against one type of UV radiation, called UVB. These are the rays most responsible for sunburn and skin cancer.
UVA radiation is different. It penetrates deep into the skin and causes premature ageing, wrinkling and age spots, as well as increasing the risk of certain skin cancers. Look for sunscreens labelled ‘broad spectrum’ that block against UVB and UVA.
It’s generally recommended you use sunscreen with an SPF between 15 and 50 (SPF ratings higher than 50 have not been proven to be more effective than SPF50). An SPF of 15 protects against about 93% of UVB rays, and an SPF of 30 protects against 97% of rays, according to the Mayo Clinic. No SPF can block 100% of UV rays.
Because some UV radiation is bound to make it through the sunscreen to your skin, the SPF number refers to about how long it would take for your skin to redden while you’re wearing the sunscreen. This means an SPF of 15 should prevent your skin from reddening for approximately 15 times longer than without the sunscreen.
Use roughly a shot-glass worth of sunscreen for each application and reapply every two hours, to ensure it actually protects your skin.