Pet Safety / Compounds / Naphthalene

Is Naphthalene safe for dogs and cats?

High risk for pets

Dogs are highly sensitive to naphthalene's hemolytic effects due to their erythrocytes' particular susceptibility to oxidative stress from naphthalene metabolites. Dogs that ingest naphthalene mothballs (a common accidental exposure — dogs are attracted to the waxy, slightly sweet-smelling balls) develop severe Heinz body hemolytic anemia, vomiting, lethargy, pale mucous membranes, hematuria (from hemolysis), and in severe cases hepatic necrosis and neurological signs. The ingestion of a single traditional naphthalene mothball (approximately 3–4 g naphthalene) by a small dog can produce life-threatening hemolytic anemia. Clinical presentation may be delayed 12–48 hours as Heinz bodies form and hemolysis progresses. Treatment requires IV fluid support, anti-emetics, and in severe cases blood transfusion. Dogs with pre-existing G6PD or glutathione deficiency would be at even greater risk, but the species-wide erythrocyte fragility makes all dogs high-risk for naphthalene ingestion. Naphthalene mothballs must be stored completely inaccessible to dogs.

What is naphthalene?

Also known as: Naphthalin, Tar camphor, White tar, Albocarbon.

IUPAC name
naphthalene
CAS number
91-20-3
Molecular formula
C10H8
Molecular weight
128.17 g/mol
SMILES
C1=CC=C2C=CC=CC2=C1
PubChem CID
931

Risk for dogs

High risk

Dogs are highly sensitive to naphthalene's hemolytic effects due to their erythrocytes' particular susceptibility to oxidative stress from naphthalene metabolites. Dogs that ingest naphthalene mothballs (a common accidental exposure — dogs are attracted to the waxy, slightly sweet-smelling balls) develop severe Heinz body hemolytic anemia, vomiting, lethargy, pale mucous membranes, hematuria (from hemolysis), and in severe cases hepatic necrosis and neurological signs. The ingestion of a single traditional naphthalene mothball (approximately 3–4 g naphthalene) by a small dog can produce life-threatening hemolytic anemia. Clinical presentation may be delayed 12–48 hours as Heinz bodies form and hemolysis progresses. Treatment requires IV fluid support, anti-emetics, and in severe cases blood transfusion. Dogs with pre-existing G6PD or glutathione deficiency would be at even greater risk, but the species-wide erythrocyte fragility makes all dogs high-risk for naphthalene ingestion. Naphthalene mothballs must be stored completely inaccessible to dogs.

Risk for cats

High risk

Cats are vulnerable to naphthalene toxicosis through two mechanisms: direct ingestion of mothballs (less common than in dogs, but possible) and inhalation/dermal absorption from stored naphthalene products in closets or drawers where cats sleep. Cats' glucuronidation deficiency impairs metabolism and elimination of naphthalene metabolites relative to dogs and humans, increasing risk from the same exposure. Clinical signs include Heinz body hemolytic anemia (similar to dogs), neurological signs (ataxia, tremors), hepatic toxicity, and respiratory signs from inhalation exposure. Cats that frequently sleep on or in naphthalene-treated clothing storage can accumulate subacute exposures. As with many volatile organic compounds, cats' grooming behavior after skin contact with naphthalene-contaminated surfaces provides an additional oral ingestion pathway. Naphthalene should not be used in any area accessible to cats; paradichlorobenzene moth repellents or cedar-based alternatives are relatively safer, though paradichlorobenzene has its own IARC Group 2B classification.

Regulatory consensus

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

AgencyYearClassificationNotes
IARC2002Group 2B (possibly carcinogenic to humans)IARC Monograph 82 (2002). Sufficient evidence in animals (Clara cell and alveolar/bronchiolar adenomas in mice at high doses; olfactory epithelium tumors in rats); limited evidence in humans. Primary concern is inhalation of naphthalene vapors from mothballs, which are practically pure naphthalene. Naphthalene is metabolized to naphthalene 1,2-oxide and then to 1-naphthol, 2-naphthol, and naphthalene dihydrodiol — some metabolites are genotoxic. Human carcinogenicity data are limited and insufficient for higher classification; the 2B classification reflects primarily the animal evidence at high inhalation exposures. Not to be confused with paradichlorobenzene mothballs (a separate compound).
US EPA1998Possible human carcinogen (Group C)US EPA IRIS assessment (1998). Naphthalene classified as a possible human carcinogen based on limited human evidence and sufficient animal evidence of carcinogenicity. EPA inhalation unit risk: 3.4 × 10⁻⁵ per μg/m³. EPA oral slope factor: 0.12/mg/kg-day. Primary regulatory concern is occupational and residential inhalation of naphthalene vapors from mothball use and combustion (coal tar, vehicle exhaust, cigarette smoke). Naphthalene is also an EPA priority HAP (hazardous air pollutant).
EPA CTX / IRIS—C (Possible human carcinogen)
EPA CTX / IRIS—Carcinogenic potential cannot be determined
EPA CTX / NTP RoC—Reasonably Anticipated to be a Human Carcinogen
EPA CTX / IARC—Group 2B - Possibly carcinogenic to humans
EPA CTX / Health Canada—Group C: IRIS (a possible human carcinogen)
EPA CTX / CalEPA—Known human carcinogen
EPA CTX / Genetox—Genotoxicity: negative (Ames: negative, 0 positive / 12 negative reports)
EPA CTX / Genetox—Genotoxicity: negative (Ames: negative, 0 positive / 12 negative reports)
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—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 sensitisation: in vivo (non-LLNA): Not likely to be sensitizing (score: low)
EPA CTX / Skin-Eye—eye irritation: in vivo: Studies Indicate No Significant Irritation (score: low)
EPA CTX / Skin-Eye—skin irritation: in vivo: Studies Indicate No Significant Irritation (score: low)

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 naphthalene

  • 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 Naphthalene:

  • Fragrance-free formulations
    Trade-offs: Consumer preference for scented products
    Relative cost: Lower (ingredient elimination)
  • Essential oil-based fragrances (with disclosure)
    Trade-offs: Natural does not mean safe — many essential oils are skin sensitizers
    Relative cost: 2-5× conventional

Frequently asked questions

Is naphthalene safe for pets?

Dogs are highly sensitive to naphthalene's hemolytic effects due to their erythrocytes' particular susceptibility to oxidative stress from naphthalene metabolites. Dogs that ingest naphthalene mothballs (a common accidental exposure — dogs are attracted to the waxy, slightly sweet-smelling balls) develop severe Heinz body hemolytic anemia, vomiting, lethargy, pale mucous membranes, hematuria (from hemolysis), and in severe cases hepatic necrosis and neurological signs. The ingestion of a single traditional naphthalene mothball (approximately 3–4 g naphthalene) by a small dog can produce life-threatening hemolytic anemia. Clinical presentation may be delayed 12–48 hours as Heinz bodies form and hemolysis progresses. Treatment requires IV fluid support, anti-emetics, and in severe cases blood transfusion. Dogs with pre-existing G6PD or glutathione deficiency would be at even greater risk, but the species-wide erythrocyte fragility makes all dogs high-risk for naphthalene ingestion. Naphthalene mothballs must be stored completely inaccessible to dogs.

What products contain naphthalene?

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

Why do regulators disagree about naphthalene?

Naphthalene has been classified by 18 agencies including IARC, US EPA, EPA CTX / IRIS, EPA CTX / IRIS, EPA CTX / NTP RoC, 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.

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Sources (3)
  1. IARC Monographs Volume 82: Some Traditional Herbal Medicines, Some Mycotoxins, Naphthalene and Styrene — Naphthalene Group 2B Evaluation (2002) — regulatory
  2. US EPA: Naphthalene — IRIS Toxicological Review, Carcinogenicity Assessment and Reference Concentrations (Group C) (1998) — regulatory
  3. ASPCA Animal Poison Control Center: Naphthalene and Mothball Toxicosis in Dogs and Cats — Heinz Body Hemolytic Anemia (2022) — veterinary

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 →