Methyl nonyl ketone
2-Undecanone
2-Undecanone (methyl nonyl ketone) is a biochemical repellent active derived from wild tomato plants (Lycopersicon hirsutum), where it serves as a natural defense against insects. It also occurs naturally in bananas, cloves, ginger, and guava. Registered by the EPA as a biochemical pesticide, it was the first new repellent active ingredient approved in over 25 years and is used in DEET-free formulas against mosquitoes and ticks.
How it works
2-Undecanone masks the cues ticks and mosquitoes use to find a host, working as a repellent rather than a toxin. In products it is the single active in BioUD, standardized at 7.75%.
Safety around dogs & cats
2-Undecanone (BioUD) has low mammalian toxicity and is actually used in some animal repellents. Incidental exposure is low risk for dogs and cats, though it is a mild irritant, so avoid the eyes and do not let a pet ingest a concentrated amount. Species-specific data are thin.
Low confidence. Ratings from ASPCA Animal Poison Control, the Pet Poison Helpline, and published veterinary toxicology. This is general information, not veterinary advice. If your pet is exposed, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435.
The evidence
The tick data are unusually strong for a plant-derived active: a 2009 study found 7.75% BioUD two to four times more repellent than DEET against three tick species, including the blacklegged tick, and a 2008 comparison rated it an effective DEET alternative on cloth. Field mosquito performance is reported around 25 to 30% DEET, though those mosquito durations come from label and field summaries rather than a clean arm-in-cage study.
- Efficacy of the new repellent BioUD against three species of Ixodid ticks2009LabWell-supported evidence
An early efficacy study of BioUD, a repellent whose active ingredient is 2-undecanone (a compound originally from wild tomato plants), tested against DEET for keeping ticks away. It pitted BioUD at its commercial 7.75% strength against DEET at 98% across three hard-tick species, including the blacklegged tick that spreads Lyme.
- Novel arthropod repellent, BioUD (2-undecanone), is an efficacious alternative to DEET2008LabWell-supported evidence
An NC State study introducing BioUD, whose active 2-undecanone comes from wild tomato, arguing that at 7.75% it matches or beats DEET against mosquitoes and ticks despite carrying far less active. It spans lab cage assays, tick choice tests, and human field trials.
Products using it
Regulatory notes
EPA-registered biochemical pesticide active ingredient (CAS 112-12-9). Originally listed via the EPA Substance Registry Services (SRS) export; classified as botanical based on its plant-derived origin (wild tomato). Not on the minimum-risk 25(b) exemption list, so products using it require EPA registration.
Safety notes
EPA reviewed 2-undecanone as a low-risk biochemical active, and the same molecule is used as a food flavoring, though concentrated material can mildly irritate skin and eyes. Companion-animal data are thin, so treat pet safety as not established.