Sunscreen works against UV rays by both reflecting and absorbing them. Inorganic materials repel the rays and the organic ones take the rays in and then shed them as heat.
8,15,30,50. If you guessed that what all of these numbers have in common is that they are grades of sunscreen, you’re right.
But, beyond that what do they really mean, and, for that matter, how does sunscreen really work, anyway?
In general, sunscreen works against UV rays by both reflecting and absorbing them. Inorganic materials like zinc oxide repel the rays and the organic ones take the rays in and then shed them as heat.
The specific UV rays sunscreen interacts with are the UV-A and UV-B varieties – sometimes one, sometimes both. Overexposure to them results in sunburns and can cause skin cancer
The numbers are the SPF, or Sun Protection Factor, representing the protection level against UV-B rays. Broad-spectrum protection indicates UV-A blocking abilities.
In their lower ranges, the SPF indicates how much longer a person can sit in the sun before getting burned than if they weren’t wearing any protection at all.
After about 30, calculating the benefits gets a little trickier. There’s very little difference between SPF 100 and SPF 50. The 100 strength blocks 99 percent of UV-B rays, and the bottle marked 50 protects against 98 percent.