When you head out into the summer sun, do you lather up with sunscreen? We hope so! It’s important to protect your skin from the sun’s ultraviolet rays.

If you’ve ever had a bad sunburn, you probably already know the value of sunscreen. Would you believe the Earth has its own form of sunscreen? It’s true! It’s called the “ozone layer.”

Way up high (between 8 and 25 miles up!) in a part of the atmosphere known as the “stratosphere,” there’s a layer of ozone. Ozone is a gas molecule made up of three oxygen atoms. Its chemical symbol is O₃.

Ozone occurs naturally in the atmosphere. It helps to protect the Earth by blocking many of the ultraviolet rays that come from the sun.

Ozone is not always good for us, though. When ozone occurs closer to the surface of the Earth, it can be an air pollutant that makes it hard to breathe and hurts trees and crops. Ground-level ozone is one of the main parts of smog that you see in many big cities.

The ozone way up high in the ozone layer, though, is very helpful. Unfortunately, the ozone layer is under attack by man-made chemicals called “ozone-depleting substances” (ODS).

Common ODS include chlorofluorocarbons (CFCs) and hydrochlorofluorocarbons (HCFCs). Many ODS could be found — and sometimes can still be found — in refrigerator and air conditioner coolants, fire extinguishers, pesticides and aerosol propellants.

When released into the air, ODS move very slowly toward the upper atmosphere. Up high, they are broken down by ultraviolet rays from the sun and release harmful molecules that destroy the “good” ozone.

ODS make the ozone layer thinner and, in some areas (such as over Antarctica), they can even create “holes” in it. When this happens, more ultraviolet light rays are allowed to pass through to the Earth.

As ultraviolet radiation on Earth increases, health issues — such as skin cancer and cataracts — increase. Ultraviolet rays can also affect food chains by reducing crop yields and harming marine organisms, which are the base of the ocean food chain.

In 1987, the United States and more than 180 other countries adopted an international treaty that called for phasing out ODS. Today, ODS have been greatly reduced.

Research shows that depletion of the ozone layer is diminishing worldwide. If the United States and other countries around the world continue to eliminate ODS, scientists believe natural ozone production should heal the ozone layer by around 2050.