Paradichlorobenzene is used as a fumigant insecticide to control clothes moths. It is also found in deodorant blocks made for trash cans and toilets. Paradichlorobenzene was first registered for use in the United States in 1942, and it is sometimes called 1,4-dichlorobenzene.

Mothballs containing paradichlorobenzene are solids that turn into toxic gas that kills moths. In 2010, there are over thirty products registered with the U.S. Environmental Protection Agency that contain paradichlorobenzene.

The vapor of paradichlorobenzene is toxic to insects. In humans and other animals, paradichlorobenzene is broken down in the body to form other compounds that may be harmful to cells or organs such as the liver.

You can be exposed to a pesticide if you breathe it in, get it on your skin, or if you accidentally eat or drink something containing a pesticide. This can happen if you get some on your hands and don't wash them before eating or smoking. People are most likely to be exposed to paradichlorobenzene by breathing in the vapors. When you smell mothballs, you are inhaling the pesticide. Small children and pets are at risk of eating mothballs, because they look like candy or other treats.

In humans, paradichlorobenzene is distributed in the blood, fat, and breast milk. It is broken down into several other chemicals by the body and excreted in urine. Human volunteers who inhaled paradichlorobenzene exhaled half the dose. The amount of paradichlorobenzene in their blood dropped by more than 50% one hour after the exposure stopped.

In animals, paradichlorobenzene is rapidly absorbed through the lungs or gut, but more slowly through the skin. Paradichlorobenzene was found in the fat, liver, and kidneys. Smaller amounts were found in the blood plasma, lungs, and muscle. Paradichlorobenzene was eliminated from the body soon after the exposure stopped. When animals were exposed for long periods of time, their bodies began to break down the paradichlorobenzene faster, and tissue levels declined.

The World Health Organization (WHO) considered paradichlorobenzene possibly carcinogenic to humans based on studies with mice. The way paradichlorobenzene caused cancer in mice could possibly occur in humans as well. The U.S. EPA has classified it as "not likely to be carcinogenic to humans".

Rats and rabbits exposed to very high doses of paradichlorobenzene vapor while pregnant gained less weight than control animals. In another study, mother rats had fewer surviving young. No information was found regarding paradichlorobenzene and asthma or other chronic diseases.

While children may be especially sensitive to pesticides compared to adults, there are currently no data to suggest that children have increased sensitivity specifically to paradichlorobenzene. Young children may be more at risk of eating mothballs because the mothballs may look like candy.

When researchers fed 10 ducks a diet containing 0.5% paradichlorobenzene for 35 days, three ducks died and the rest did not grow as well. Paradichlorobenzene is moderate to low in toxicity to fish, with differences in sensitivity by species. No information was found for the effects of paradichlorobenzene on bees.