Daily sunscreen use is essential to protecting your skin from the sun’s harmful rays, but it is equally important to be educated on proper sunscreen use. In honor of Melanoma Awareness Month, Dr. Fening breaks down all of the acronyms and other terms you need to know when choosing and using your sunscreen.


The sun emits many different types of rays, the most harmful of which are ultraviolet A (UVA) and ultraviolet B (UVB) rays. UVB rays cause sunburns and can cause skin cancers, including melanoma. UVA rays penetrate deeper into the skin and can pass through window glass. UVA rays cause a suntan, but are also involved in photoaging (wrinkles) and skin cancer formation. Because both UVA and UVB exposure leads to skin cancer, it is important to protect the skin from both.


SPF (Sun Protection Factor) is a measure of a sunscreen’s ability to protect from UVB rays. Technically speaking, it represents the amount of time it would take to develop a sunburn when the sunscreen is applied compared to unprotected skin. For example, let’s say it would take 10 minutes of sun exposure to develop a sunburn in unprotected skin. If a sunscreen with an SPF of 30 was applied, it would take 30 times longer (or 10 minutes x 30 = 300 minutes) to develop a sunburn. It’s important to note that SPF only measures protection against UVB rays. To know if a sunscreen also provides UVA protection, look for the label to say “broad spectrum.”

Chemical vs. Physical Sunscreen

There are two main types of sunscreen – chemical blockers and physical blockers. Chemical blockers work by absorbing UV rays, like a sponge. Physical blockers work by blocking UV rays, like a shield. There are benefits of each type, and most sunscreens have a combination of chemical and physical blockers. However, for babies and those with sensitive skin, choose a sunscreen with only physical blockers (zinc oxide and titanium dioxide).


Sunscreen should be applied to the skin prior to sun exposure and reapplied every two hours. There is no such thing as a “waterproof” sunscreen, but some sunscreens have been tested to be “water-resistant.” This means they will protect your skin in the water, but only for about 40 minutes. When swimming, sunscreen should be reapplied after 40 minutes.

More frequent reapplication is also necessary when sweating. To help prevent sunscreen from running off of your skin when exercising/sweating, look for water-resistant and oil-free sunscreens. Choose physical sunscreens (instead of chemical), which are less likely to run into the eyes and cause stinging. Powdered sunscreens are also a great option.


Sun protective clothing is becoming increasingly popular. UPF (Ultraviolet Protection Factor) measures the amount of UV radiation that can penetrate clothing and reach the skin. While a white cotton t-shirt only offers a UPF of about 7, several companies now make clothing with UPF 50 that are specifically designed to keep you cool and comfortable while protecting against harmful UV rays.