Summary from
I N S E C T I C I D E S Y N E R G I S T F A C T S H E E T by C. Cox,
Journal of Pesticide Reform, Summer 2002 Vol 22, No. 2 BY CAROLINE COX

For the whole article, see listing of PIPERONYL BUTOXIDE 2002
on the web page at .
Look under under Pesticide Fact Sheets.

Piperonyl butoxide (PBO) is a synergist used to increase the potency of insecticides like pyrethrins and pyrethroids. According to the U.S. Environmental Protection Agency (EPA), PBO is one of the most commonly used ingredients in household pesticide products.

PBO acts as a synergist by inhibiting the activity of a family of enzymes called P450s. These enzymes have many functions, including breakdown of toxic chemicals and transformation of hormones.

Symptoms of PBO exposure include nausea, diarrhea, and labored breathing. EPA classifies PBO as a "possible human carcinogen" because it caused liver tumors and cancers in laboratory tests.

In a study conducted by PBO manufacturers, PBO caused atrophy of the testes in male rats. Other researchers found behavioral changes (a decrease in home recognition behavior) in the offspring of exposed mothers.

PBO affects a variety of hormone-related organs, including thyroid glands, adrenal glands and the pituitary gland.

PBO reduces the immune response of human lymphocytes, cells in our blood that help fight infections.

Concentrations of less than one part per million of PBO reduce fish egg hatch and growth of juvenile fish. PBO also inhibits hormone-related enzymes in fish and slows the breakdown of toxic chemicals in their tissues. PBO is very toxic to earthworms and highly toxic to aquatic animals.