Pyriproxyfen mimics a natural hormone in insects and disrupts their growth. It is a type of insect growth regulator that affects mostly young insects and eggs. Pyriproxyfen affects many types of insects, including fleas, cockroaches, ticks, ants, carpet beetles, and mosquitoes. It has been registered for use in pesticides by the Environmental Protection Agency (EPA) since 1995.

Pyriproxyfen is found in more than 300 registered pesticide products. These include products used inside homes and on lawns. Many products are also used in agriculture as leaf treatments on food crops. Pyriproxyfen is commonly used directly on pets to control fleas and ticks.

Pyriproxyfen products can come in many forms, including liquids, granules, dusts, and pellets. Other products are used in aquatic settings like birdbaths and ponds. Some materials are infused with pyriproxyfen, such as pet flea collars. Products with pyriproxyfen often include other insecticides to kill adult insects.

Pyriproxyfen is an insect growth regulator. It mimics natural insect hormones that stop young insects from maturing into adults. Pyriproxyfen can affect an insect if it is touched or eaten. However, pyriproxyfen is rarely toxic to adult insects. Instead, it disturbs egg-laying and egg-hatch and keeps young insects from growing into adult forms. This prevents target insects from multiplying.

You may be exposed to pyriproxyfen by eating it, touching it, inhaling it, or getting it in your eyes. This could happen while applying outdoor products during windy weather. It could also happen if you use a product and don’t wash your hands before eating or smoking. Your skin may also be exposed if you touch a treated pet. You can limit exposure to pesticide products by carefully following label instructions.

You may be exposed to pyriproxyfen by eating very small amounts of it as residue found on food. Pyriproxyfen is used on many foods, including asparagus, peanuts, strawberries, and grapes. To reduce pesticide residues on fresh foods, consider these tips.

If eaten, pyriproxyfen is partially absorbed by the gut. Once inside, much of it is quickly broken down and leaves the body. In studies with rats, more than three quarters left the body within seven days. However, very small amounts of pyriproxyfen can be stored in fat and breast milk in the body. There are no studies for skin absorption of pyriproxyfen. However, other skin and developmental studies with pyriproxyfen suggest that less than one-third is absorbed through skin.

In one study, two groups of lactating goats were fed pyriproxyfen for five days. Extremely small amounts of pyriproxyfen were found in their milk. Two groups of laying hens were fed pyriproxyfen for eight days. A very small amount of the dose was found in the eggs, with most in the yolks.

Mice and rats fed pyriproxyfen in their diets for 1.5 to 2 years did not show evidence of cancer after these studies. After several studies, pyriproxyfen has not shown evidence of altering or damaging genes. Based on these studies, the EPA has classified pyriproxyfen as not likely to cause cancer in humans.

In one study, dogs were fed moderate to high amounts of pyriproxyfen in their diet every day for one year. At the two highest dose levels, some animals became very thin and had fewer blood cells. Animals in all groups had increased cholesterol and liver weights. In another one-year study, dogs were fed small amounts of pyriproxyfen and there were no deaths or illnesses. In long-term feeding studies with rats, mice, and dogs, there were effects on the liver and kidneys.

In one study, rats fed high doses of pyriproxyfen during pregnancy did not have any effects on their young. Similarly exposed rabbits had reduced birth rates only at the highest dose tested. In another study with rats, some young had unusual skeletal and digestive changes.

Pyriproxyfen has been evaluated for its potential as an endocrine disruptor by the EPA. These studies did not find convincing evidence of interaction with the estrogen pathway. When male rats were fed pyriproxyfen for several weeks, there was some evidence of interaction with the androgen and thyroid pathways.

Children may be especially sensitive to pesticides compared to adults. Based on developmental studies, the EPA determined that infants and children are not more sensitive to pyriproxyfen than adults. However, young children may act in ways that put them at greater risk of being exposed. For example, they may spend more time near the floor. They may also be more likely to place their hands in their mouths after touching treated surfaces or pets.

Pyriproxyfen is practically nontoxic to birds, mammals, and adult honeybees. However, eggs and larval stages of honeybees and other insects are much more likely to be sensitive than adults. Bumble bee colonies fed a moderate dose of pyriproxyfen and sugar for 24 hours developed normally over five weeks.

In fish, pyriproxyfen is moderately to highly toxic, depending on the species. However, two species of fish exposed to pyriproxyfen-treated water showed no toxic effects, even at the highest dose. It is difficult to tell how toxic pyriproxyfen is to fish because it dissolves poorly in water. Pyriproxyfen has a moderate potential to bioaccumulate in fish because it can be stored in fat.