Sunblock is a thick cream or lotion you spread on your skin to protect it from the sun's harmful rays. When you're going to be outside on a sunny day, especially at the beach or playing sports, sunblock acts like an invisible shield that stops ultraviolet light from damaging your skin.

The sun gives off different types of light, including ultraviolet (or UV) rays that you can't see but that can hurt your skin. Too much sun exposure causes painful sunburns in the short term and can lead to serious skin problems years later. Sunblock contains special ingredients that either absorb these rays before they reach your skin or reflect them away, like a microscopic mirror.

You'll see sunblock bottles marked with numbers like SPF 30 or SPF 50. SPF stands for “sun protection factor,” and higher numbers mean stronger protection. Dermatologists (doctors who specialize in skin) recommend applying sunblock about 30 minutes before going outside and reapplying it every couple of hours, especially after swimming.

People sometimes use sunblock and sunscreen interchangeably. Either way, both protect your skin so you can enjoy outdoor activities safely.