Piperonyl butoxide (PBO) is not an insecticide itself - it is a synergist that makes other insecticides 3-10x more effective. It works by blocking the enzymes insects use to detoxify pesticides, essentially disabling their defense system. Found in most pyrethrin products, many permethrin formulations, and some professional spray mixes.
PBO does not kill insects on its own. It enhances the effectiveness of pyrethrins (3-5x boost), pyrethroids (2-3x boost in resistant populations), and some other insecticide classes. Most valuable against insecticide-resistant populations where the insect enzymes are actively detoxifying the killing agent.
PBO is an ingredient in products, not sold alone to consumers. Found in: most pyrethrin aerosols (CB-80, PT 565, PyGanic), many flea sprays, lice treatments, bed bug sprays (Bedlam Plus), some professional concentrates. When you see pyrethrin products listing two active ingredients - pyrethrins AND piperonyl butoxide - the PBO is the synergist.
Low mammalian toxicity. PBO has been used in consumer products since the 1950s with an excellent safety record. Found in human head lice treatments applied directly to children. The EPA classifies it as a Group C possible human carcinogen based on high-dose animal studies, but real-world exposure levels are far below concern thresholds.
How insects detoxify pesticides: Insects produce cytochrome P450 enzymes (mixed-function oxidases) in their gut and fat body that chemically modify insecticide molecules, rendering them harmless. This is the same enzyme system that detoxifies plant chemicals in the insects natural diet. PBO jams this defense system by binding to P450 enzymes irreversibly, leaving the insecticide free to reach its target in the nervous system.
Resistance management: In insecticide-resistant pest populations, P450-based metabolic resistance is one of the most common mechanisms. Adding PBO can partially or fully restore the effectiveness of insecticides against resistant populations. This is why many bed bug spray products include PBO - bed bug populations have developed significant pyrethroid resistance, and PBO helps overcome it.
Reading labels: When you see a product listing Pyrethrins 0.5% + Piperonyl Butoxide 4.0%, the PBO concentration is intentionally much higher than the pyrethrin concentration because the synergistic effect requires an excess of PBO relative to the active insecticide.
PBO with pyrethroids: While PBO is most commonly paired with natural pyrethrins, it also synergizes synthetic pyrethroids - particularly against resistant populations. Products like Bedlam Plus (sumithrin + PBO) and some professional tank mixes exploit this to improve performance against pyrethroid-resistant bed bugs and cockroaches.