To pollute means to make something dirty, harmful, or unsafe by adding unwanted substances to it. When factories pollute the air by releasing smoke and chemicals, they're making it harder to breathe and damaging the atmosphere. When trash pollutes a river, it harms the fish and plants living there and makes the water unsafe to drink.

Pollution happens when harmful materials get into places they don't belong: oil spills pollute oceans, plastic waste pollutes beaches, and loud noise can even pollute the peace of a quiet neighborhood. The substances that cause pollution are called pollutants. Car exhaust, industrial waste, and pesticides are all pollutants.

People can pollute accidentally, like when litter blows away before you can pick it up, or carelessly, like when someone dumps garbage in a forest instead of disposing of it properly. Throughout history, as cities and industries grew, pollution became a serious problem. In the 1800s, factory smoke turned London's air black. Today, scientists work to understand how pollution affects our planet and our health, while engineers develop cleaner technologies.

The word can also describe corrupting something non-physical. Someone might say that gossip pollutes a friendship or that constant negativity pollutes the atmosphere of a classroom, meaning these things introduce harmful influences into something that should be healthy or positive.