Mothballs poisoning in dogs and cats
Toxic agent: Naphthalene or paradichlorobenzene — and which one matters · Reviewed 2026-08-18
Phone a vet now, before reading on. Have ready: your pet's weight, roughly how much was eaten and when, and the packaging if there is any. ASPCA Animal Poison Control (+1 888 426 4435), Pet Poison Helpline, or Animal PoisonLine in the UK.
Two chemicals are sold as mothballs and one is roughly twice as toxic as the other. A single naphthalene ball can poison a small dog; the smell alone will not tell you which you have.
What it actually does
Naphthalene oxidises haemoglobin, causing methaemoglobinaemia and destruction of red blood cells, and it damages the liver. Paradichlorobenzene is less toxic and mainly causes vomiting and central nervous system depression, though large amounts affect the liver too. Both are also irritating to the gut on the way through.
How much matters
How to work out which you are dealing with:
| Naphthalene | the older type, roughly twice as toxic; one ball can be a serious dose for a small dog |
|---|---|
| Paradichlorobenzene | more common in modern products, less toxic |
| The float test | in a solution of water and a lot of salt, naphthalene tends to float and paradichlorobenzene tends to sink — do this only if you can do it safely and quickly |
| Better | read the packaging, or bring it in |
Also consider what the mothballs were doing: stored clothing and blankets absorb the chemical, so a cat sleeping on a stored blanket has a prolonged low-level exposure rather than a single ingestion.
What you will see, and when
Onset: Within a few hours. Typical course: 24 to 72 hours.
- 1–4 hoursVomiting, a strong chemical smell on the breath, drooling
- 4–12 hoursLethargy, wobbling, tremors, pale or brown-tinged gums
- 12–72 hoursAnaemia, jaundice, dark urine, liver and kidney injury; seizures in severe cases
What the vet will do
Decontamination — but not by inducing vomiting where aspiration is a risk. Activated charcoal, intravenous fluids, oxygen, and for naphthalene methaemoglobinaemia, N-acetylcysteine, ascorbic acid or methylene blue depending on species and severity. Blood counts and liver values monitored.
Outlook
Good for paradichlorobenzene and small naphthalene exposures. Guarded for a naphthalene ingestion in a small animal.
Dogs and cats are not the same here
Both. Cats are more susceptible to methaemoglobinaemia and more likely to have chronic exposure via stored bedding.
Where it comes from in a normal house
- Wardrobes, drawers and stored winter clothing
- Loft insulation and stored boxes
- Toilet and urinal deodorant blocks, which are often paradichlorobenzene
- Some outdoor pest deterrents used against snakes and squirrels
The thing people get wrong
“They are just strong-smelling — it will taste awful and they will spit it out.”
Dogs do swallow them, and cats get exposed through bedding rather than by eating anything. The smell is not a deterrent, and the chemical does not need to be eaten in quantity to matter.
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How much Mothballs is dangerous?
Also consider what the mothballs were doing: stored clothing and blankets absorb the chemical, so a cat sleeping on a stored blanket has a prolonged low-level exposure rather than a single ingestion.
How long after exposure to Mothballs do symptoms start?
Within a few hours. Vomiting, a strong chemical smell on the breath, drooling. 24 to 72 hours.
Is Mothballs worse for cats or dogs?
Both. Cats are more susceptible to methaemoglobinaemia and more likely to have chronic exposure via stored bedding.
Is it true that: They are just strong-smelling — it will taste awful and they will spit it out.
Dogs do swallow them, and cats get exposed through bedding rather than by eating anything. The smell is not a deterrent, and the chemical does not need to be eaten in quantity to matter.
Related emergencies
Sources
This page is information, not veterinary advice. Toxic doses vary with body weight, age, breed and individual sensitivity, and the figures above exist to explain what a vet is assessing, never to decide that an amount is safe. If you are reading this because something has already been eaten, call a vet.