At a glance
| Chemical family | Methylenedioxyphenyl synergist — cytochrome P450 inhibitor (enhances pyrethroid/pyrethrin potency) |
| CAS number | 51-03-6 |
| Classification | Not IARC classified. EPA Group C (possible human carcinogen — based on hepatocellular tumours in mice). Inhibits cytochrome P450 enzymes. Not an insecticide itself — a synergist |
| Where you encounter it | Combined with pyrethroids/pyrethrins in bed bug sprays, flea sprays, lice treatments, household insecticides, and agricultural formulations. House dust (especially after pest treatment) |
| Sleep micro-environment relevance | Present in most pyrethroid bed bug spray formulations applied to mattresses and bed frames. Detected in house dust. Inhibits the same P450 enzymes that humans use to detoxify other chemicals |
Regulatory & certification status
| European Union | Not approved as a plant protection active substance (not renewed). Authorised under the Biocidal Products Regulation as a synergist in insecticide products. Regulatory |
| United States | EPA-registered synergist for use with pyrethroids and pyrethrins. Group C (possible human carcinogen). Present in most OTC bed bug spray formulations. Regulatory |
| Canada | PMRA-registered synergist. Present in pest control and lice treatment products. Regulatory |
| International | Not IARC classified. EPA Group C. The most widely used insecticide synergist globally. Used in WHO-approved insecticide formulations for malaria control. Regulatory |
What it is
Piperonyl butoxide is a semi-synthetic compound derived from safrole (a natural product from sassafras). It contains a methylenedioxyphenyl group that inhibits cytochrome P450 mixed-function oxidases — the same family of enzymes that insects (and humans) use to metabolise and detoxify foreign chemicals. By blocking P450 enzymes in insects, PBO prevents them from breaking down pyrethroids and pyrethrins, making the insecticide 2-10 times more effective. This synergism allows lower insecticide concentrations to be used. PBO has been used in insecticide formulations since the 1940s. IARC has not evaluated PBO. The EPA classified it as Group C based on hepatocellular tumours in mice at high doses. The P450 inhibition mechanism raises a broader concern: PBO exposure may also inhibit human P450 enzymes, potentially affecting the metabolism of other chemicals, drugs, and environmental contaminants.
Where it shows up in bedding
PBO enters the bedroom as a component of pyrethroid bed bug sprays applied to mattress seams, bed frames, and baseboards. Most commercial bed bug spray formulations combine a pyrethroid (permethrin, cypermethrin, or deltamethrin) with PBO as a synergist. After application, PBO residues remain on treated surfaces alongside pyrethroid residues. PBO is also present in flea sprays applied to carpets and pet bedding, and in lice treatment shampoos that may leave residues on pillowcases. House dust surveys detect PBO at significant concentrations, particularly in homes that have undergone recent pest treatment. During sleep, exposure occurs through dermal contact with treated mattress surfaces and inhalation of resuspended particles.
Citations
- Horton, M.K. et al. (2011). Impact of Prenatal Exposure to Piperonyl Butoxide and Permethrin on 36-Month Neurodevelopment. Pediatrics, 127(3): e699-e706. Source Peer-reviewed
- EPA. Piperonyl Butoxide (PBO) — Pesticide Fact Sheet. Source Regulatory
- ATSDR (2003). Toxicological Profile for Pyrethrins and Pyrethroids. Source Regulatory
Frequently asked questions
Does PBO make bed bug sprays more toxic to humans?
PBO enhances the toxicity of pyrethroids to insects but does not significantly increase acute toxicity to humans at the concentrations used in consumer products. However, PBO inhibits cytochrome P450 enzymes, which are part of the human detoxification system. This means PBO exposure could theoretically affect how the body metabolises other chemicals, drugs, or environmental contaminants. The practical significance of this at residential exposure levels is not well established.
Why is PBO in most bed bug sprays?
Bed bugs have developed resistance to pyrethroids through metabolic mechanisms — they upregulate P450 enzymes to break down the insecticide faster. PBO counters this resistance by inhibiting those P450 enzymes, restoring the pyrethroid's effectiveness. Without PBO, many pyrethroid products would be significantly less effective against resistant bed bug populations.
Related compounds
Embr is a sleep environment company researching and addressing the chemistry of the bedroom. Research and product development in progress.
Last reviewed 2026-07-08. If you find a factual error, contact us.