Pet Safety / Compounds / Malathion

Is Malathion safe for dogs and cats?

Elevated risk for pets

Dogs are susceptible to organophosphate toxicity at doses proportionally lower than humans due to lower plasma cholinesterase reserves and grooming behavior (licking treated fur). Malathion-containing flea and tick dips and sprays were historically used in veterinary practice but have been largely superseded by newer formulations. Clinical signs of acute malathion poisoning: salivation, lacrimation, urination, defecation (SLUD), muscle tremors, seizures. Treatment: atropine + pralidoxime. Current veterinary use is uncommon but accidental exposure from agricultural spraying or treated lawns remains a risk.

What is malathion?

The IUPAC name is diethyl 2-dimethoxyphosphinothioylsulfanylbutanedioate.

Also known as: diethyl 2-dimethoxyphosphinothioylsulfanylbutanedioate, Carbophos, Carbofos, Mercaptothion.

IUPAC name: diethyl 2-dimethoxyphosphinothioylsulfanylbutanedioate
CAS number: 121-75-5
Molecular formula: C10H19O6PS2
Molecular weight: 330.4 g/mol
SMILES: CCOC(=O)CC(C(=O)OCC)SP(=S)(OC)OC
PubChem CID: 4004

Risk for dogs

Elevated risk

Risk for cats

Elevated risk

Cats are more sensitive to organophosphate toxicity than dogs. Deficient hepatic CYP450 enzyme complement and glucuronidation capacity reduces detoxification. Malathion-containing dips are contraindicated in cats; even product residue from treated dogs can cause secondary intoxication in cats through grooming. Malathion has a narrow safety margin in cats. Historical malathion-based flea products caused cat fatalities and were withdrawn. Agricultural drift and lawn-treated grass are current risk scenarios.

Regulatory consensus

15 regulatory and scientific bodies have classified Malathion. The classifications differ — that's the data.

Agency	Year	Classification	Notes
IARC	2015	Group 2A (probably carcinogenic to humans)	IARC Monograph 112 (2015). Limited evidence in humans for non-Hodgkin lymphoma; sufficient evidence in experimental animals. One of the most controversial IARC reclassifications; spawned significant public debate given widespread consumer use in home insect control and public health spraying programs (West Nile, Zika).
US EPA	2009	suggestive evidence of carcinogenicity, but not sufficient to assess human carcinogenic potential	EPA Reregistration Eligibility Decision (RED) 2009; EPA did not classify malathion as carcinogenic under current cancer guidelines. EPA continues to permit use in food and non-food settings with established tolerances. Regulatory disagreement with IARC Group 2A classification reflects different weight-of-evidence frameworks.
EPA CTX / IARC	—	Group 2A - Probably carcinogenic to humans
EPA CTX / EPA OPP	—	Suggestive Evidence of Carcinogenicity but Not Sufficient to Assess Human Carcinogenic Potential
EPA CTX / CalEPA	—	Known human carcinogen
EPA CTX / Genetox	—	Genotoxicity: positive (Ames: negative, 4 positive / 7 negative reports)
EPA CTX / Genetox	—	Genotoxicity: positive (Ames: negative, 4 positive / 7 negative reports)
EPA CTX / Skin-Eye	—	Skin Sensitization: Skin Sens. 1 (score: high)
EPA CTX / Skin-Eye	—	Eye Irritation: Category 2B (score: moderate)
EPA CTX / Skin-Eye	—	Skin Irritation: Not classified (score: low)
EPA CTX / Skin-Eye	—	Skin Sensitization: Category 1 (score: high)
EPA CTX / Skin-Eye	—	Skin Sensitization: Skin Sens. 1 (score: high)
EPA CTX / Skin-Eye	—	Eye Irritation: Category 6.4A (Category 2A) (score: high)
EPA CTX / Skin-Eye	—	Skin Irritation: Category 6.3B (Category 3) (score: moderate)
EPA CTX / Skin-Eye	—	Skin Sensitization: Category 6.5B (Category 1) (score: moderate)

Regulators apply different standards of evidence — animal-data weighting, exposure-pattern assumptions, epidemiological power thresholds — which is why two scientific bodies can review the same data and reach different conclusions. The disagreement is the data.

Where pets encounter malathion

Industrial Facilities — Manufacturing plants, Chemical storage areas, Waste treatment sites
Occupational Environments — Factories, Warehouses, Transportation vehicles

Safer alternatives

Lower-risk approaches that achieve a similar outcome to Malathion:

Physical/mechanical pest control (IPM)
Trade-offs: More labor-intensive. May not be sufficient for severe infestations.

Relative cost: Variable; lower long-term

Frequently asked questions

Is malathion safe for pets?

What products contain malathion?

Malathion appears in: Manufacturing plants (Industrial facilities); Chemical storage areas (Industrial facilities); Factories (Occupational environments); Warehouses (Occupational environments).

Why do regulators disagree about malathion?

Malathion has been classified by 15 agencies including IARC, US EPA, EPA CTX / IARC, EPA CTX / EPA OPP, EPA CTX / CalEPA, with differing conclusions. Regulators apply different standards of evidence (animal data weighting, exposure-pattern assumptions, epidemiological power thresholds), which is why two scientific bodies can review the same data and reach different conclusions. See the regulatory consensus table on this page for the full picture.

See Malathion in the pets app

Look up products containing malathion, compare to alternatives, and explore the full data record.

Open in pets View raw API data

Sources (4)

IARC Monographs Volume 112: Malathion and Diazinon (2015) — regulatory
US EPA Reregistration Eligibility Decision (RED) for Malathion (2009) — regulatory
ATSDR Toxicological Profile for Malathion (2003) — report
ASPCA Animal Poison Control Center: Organophosphate Toxicosis in Companion Animals (2018) — report

Reference data, not professional advice. Aggregates publicly available regulatory and scientific data; not a substitute for veterinary, medical, legal, or regulatory advice. Why we built ALETHEIA →