Imagine a day of frolicking at the sunny beach—one of the joys of summer! While writing The Mystery of Science: Astronomy, I learned about our Sun and the amazing way it provides just the right amount of light and warmth to sustain life on Earth. Sunlight contains not only heat and visible light energy but also a different type of energy called ultraviolet (UV) radiation. We can’t see UV radiation, but it can penetrate and harm our skin cells. Earth’s atmosphere protects us from some of these rays, but those that reach the surface can still cause skin damage that may eventually lead to skin cancer.

Enter sunscreen—a thin barrier that can do wonders in protecting you from the Sun’s UV rays. It forms a protective layer between your skin and the Sun’s rays in different ways, depending on the type of sunscreen you use.

Know Your Sunscreen

Sunscreen was invented in the early 1930s. There are two main types, and each protects our skin in a different way. The first type is an absorber—a chemical sunscreen that contains ingredients such as avobenzone or oxybenzone. These chemicals absorb UV rays; their molecules become energized, and the energy is released as a tiny amount of heat.

The second type is a blocker and absorber—a mineral sunscreen that blocks some UV rays and reflects or scatters others. An example is zinc oxide, the white substance often seen on a lifeguard’s nose. Whether you choose an absorber or a blocker, experts agree that sunscreen is an important tool for protecting your skin.

What About SPF?

SPF stands for Sun Protection Factor. The higher the SPF, the more UVB rays are blocked or absorbed. SPF 15 blocks about 93% of the Sun’s UVB rays, while SPF 50 blocks about 98%. Most experts recommend using a sunscreen with at least SPF 30 for adequate protection.

Even More Important…

Even more important than the SPF number is how you apply your sunscreen. Most people use only about half the amount needed for proper protection. Be sure to apply it generously—this is not a situation where a little goes a long way.

You should also reapply sunscreen regularly. A single application at the beginning of a long day of biking in the sun will not be enough. Because sweating, swimming, and even towel-drying can remove sunscreen, experts recommend reapplying it every two hours, or more often if you are swimming or perspiring heavily.

Other Ways to Protect Yourself

If you don’t want to use sunscreen—or find yourself without it—there are other ways to create a barrier between your skin and the Sun’s rays. Choose clothing that minimizes sun exposure, such as a wide-brimmed hat or a swim shirt. You can also wear UV-blocking sunglasses to protect your eyes.

Simply sitting in the shade can help reduce sun exposure, but don’t be fooled by a cloudy or cool day. UV rays can pass through clouds, and snow can reflect UV radiation, increasing your exposure.

So the next time you’re out in the Sun, enjoy the warmth God has provided, but also protect yourself from harmful UV rays. And when you apply sunscreen, you’ll know that millions of tiny molecules are hard at work absorbing, blocking, or scattering those rays before they can damage your skin.