Limonene
Cyclohexene, 1-methyl-4-(1-methylethenyl)-
Limonene is the citrus-peel terpene behind lemon and orange oils. It kills and knocks down insects as a registered insecticide, but it has no track record as a skin repellent for people, and it is toxic to cats.
How it works
d-Limonene acts on insect nerve receptors as a contact toxin rather than masking host odor. That makes it useful for killing insects but not a demonstrated topical repellent.
Safety around dogs & cats
d-Limonene, the citrus terpene, is a classic cat hazard: concentrated citrus-oil dips have caused drooling, tremors, low body temperature, and unsteadiness in cats, which detoxify it slowly. Never apply citrus oil to a cat. Dogs tolerate more but concentrated oil still irritates and upsets the stomach.
High 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 limonene literature covers insecticidal and larvicidal action, not human bite protection; no credible skin complete-protection-time data support it as a repellent. It appears in a single botanical product in our set.
- Toxicology of selected pesticides, drugs, and chemicals. D-limonene, linalool, and crude citrus oil extracts1990Review
A short veterinary review of the toxicology of d-limonene, linalool, and crude citrus oil extracts used in insecticidal pet products, focused on why cats react badly to them.
- Effects of an insecticidal dip containing d-limonene in the cat1986Lab
A controlled experiment applying a d-limonene insecticidal dip to cats at escalating strengths to map the dose at which citrus-oil toxicity appears.
Products using it
Regulatory notes
Source: EPA SRS active ingredient list export. Minimum risk (25(b)) status is applied separately when applicable.
Safety notes
Oxidized limonene is a common skin sensitizer, and citrus terpenes are documented cat toxins (hypersalivation, tremors, ataxia); see the pet-safety note below.