Though some people use the word interchangeably, sunscreen is not the same thing as sunblock. Sunscreen is a compound made of both organic and inorganic chemicals that you spread on your skin to keep certain light from reaching deeper layers of your skin. Sunscreens keep some light rays from penetrating your skin, but not all of them. Sunscreens act like screen doors in a way, letting some of the light through, but not all. Sunscreens filter out harmful UV rays, the ones that are the biggest culprits in harming the skin and initiating a melanin response.
Sunblock is also a compound of organic and inorganic chemicals that you spread on your skin, but instead of letting some light through, they completely block, reflect or scatter all light so no sun rays reach your skin. Most sunblocks contain zinc oxide or titanium oxide. You may remember having seen lifeguards at the beach or pro athletes with white “stuff” spread on their nose and cheeks. That is characteristic of white zinc oxide, a popular & traditional sunblock. Today, sunblocks aren’t always opaque, as the oxide particles have been made smaller and less detectable visibly.
Most sunscreens contain sunblocks as one of their active ingredients.
Sunscreens contain organic molecules that filter or block UV radiation, a type of light emitted by the sun that humans are unable to see. There are three different kinds of UV light: UV-A, UV-B and UV-C.
UV-A light is able to penetrate the skin and get down to deeper levels of the skin tissue. This is the UV light responsible for cancer and premature skin aging. UV-B light is responsible for tanning your skin and for sunburns. Sunburns can result in skin cancers years later in life. UV-C light is absorbed by the earth’s atmosphere and does not reach the surface or our skin.
Different organic molecules absorb different types of UV light and release it as heat. The most common organic molecules in today’s sunscreens are:
Absorb both UV-A and UV-B
SPF is an abbreviation of “Sun Protection Factor”. It is a number used to gauge how many hours you can safely stay out in the sun without getting sunburn. SPF does not indicate whether a sunscreen protects you from UV-A rays.
Every person has a “natural” SPF. If you have darker skin with more melanin, you can stay out longer in the sun without burning than a person with lighter skin that contains less melanin. Although not completely accurate, an easy way to think of SPF is based on multiplication. If you can normally stay out in the sun for 10 minutes without burning, then using a sunscreen with a SPF of 10 will allow you to stay out in the sun 10 times longer, or 100 minutes.
Though SPF only applies to UV-B light, most sunscreen products will indicate on their labels whether or not they also block UV-A rays. Be sure to use a sunscreen that protects against both. A sunscreen that blocks both is called “broad spectrum” and you should make sure your sunscreen says this on the bottle. Sunblocks reflect both UV-A and UV-B rays.
Below are sunscreen/sunblock products recommended by MidState Skin Institute: