Q: What does #SPF really mean? Is SPF 100 really that much better than SPF 30?
A: SPF or sun protection factor describes the sunscreen’s ability to block ultraviolet B (UVB) rays which cause both sunburns and skin cancer.
SPF is measured by applying sunscreen to a volunteer in a laboratory and measuring how much longer it takes the volunteer to get burned. For example, if it normally takes 5 minutes for someone to get a sunburn with SPF 10 it will now take 50 minutes.
It is important to remember SPF only refers to UVB and NOT UVA rays, so make sure to get a sunscreen that says broad-spectrum which means it also blocks UVA rays. As for how high an SPF you need, SPF 30 is generally good enough as there isn’t that much of a benefit above SPF 30 as it blocks 97% of UVB rays, SPF 50 blocks 98% and SPF 100 blocks 99%.
To get that protection you need to make sure you apply enough sunscreen as most people only apply 25-50% of the sunscreen needed. Remember that most adults will need one ounce or approximately a shot glass amount of sunscreen to cover their body and a teaspoon amount to cover their face.