The strength of sunscreen is measured by Sun Protection Factor (SPF). SPF measures the protection from UVB rays that cause sunburns.
There are two different types of sunscreen — physical and chemical. Physical and chemical sunscreens both protect the skin from the sun’s harmful UV rays by preventing the them from contacting the skin. Many modern sunscreens work by using a combination of physical and chemical blockers to provide UV protection.
Physical sunscreens are created from the naturally occurring minerals titanium oxide and zinc oxide, which are ground down into fine powders. These minerals protect the skin by reflecting both UVA and UVB rays away from the skin.
Physical sunscreens work for most people because they are less likely to cause allergic reactions or skin irritation for anyone who has sensitive skin. Generally, people who have conditions like post inflammatory hyper-pigmentation from acne or other discolorations like melasma should use physical sunscreen because they offer broad-spectrum coverage.
Older physical sunscreens left a white sheen on medium and darker skin tones but recent formulations are much more natural looking on all skin tones.
Chemical sunscreens contain organic compounds that have been developed to absorb the energy from UV light and change this energy into heat so it doesn’t damage the skin. These types of sunscreen also rub in much better and leave no obvious discoloration on the skin.
Chemical sunscreens used to have a more narrow UV coverage range but many now cover both UVA and UVB rays. Look for the phrase” broad spectrum coverage” on the bottle if you are unsure.
Physical and chemical sunscreens both do a good job at protecting the skin as long as they are applied and reapplied generously every day.