Mothball exposure becomes dangerous at surprisingly small amounts, especially for children, pets, and people with certain genetic conditions. A single naphthalene mothball, which typically weighs around 5 grams, contains enough chemical to cause serious harm if swallowed by a young child. Even without ingestion, breathing mothball fumes in poorly ventilated spaces over hours or days can cause headaches, nausea, and damage to red blood cells.
The danger depends on which chemical the mothball contains, how you’re exposed (swallowing vs. breathing fumes vs. skin contact), and how long the exposure lasts. Here’s what you need to know about each scenario.
What’s Actually in Mothballs
Mothballs sold in the United States contain very high concentrations of either naphthalene or paradichlorobenzene as active ingredients. Both are solid pesticides that slowly release toxic gas designed to kill clothes moths and other fabric-eating insects. They are meant to be used only in closed, airtight containers where the fumes build up and stay trapped. Using them in open spaces, attics, gardens, or anywhere other than a sealed container is actually illegal under EPA regulations, because the product label restricts where they can be placed.
Of the two chemicals, naphthalene is significantly more toxic. Paradichlorobenzene is the milder option: adults have tolerated ingestions of up to 20 grams without serious effects. That said, “less toxic” doesn’t mean safe, and chronic exposure to either chemical carries health risks.
How Much Ingestion Is Dangerous
For naphthalene mothballs, as little as 1 to 2 grams can potentially cause drowsiness or seizures. That’s less than half a standard mothball. The threshold drops dramatically for people with G6PD deficiency, a common inherited enzyme condition affecting roughly 400 million people worldwide. In those individuals, as little as 250 to 500 milligrams of naphthalene (a fraction of a single mothball) can trigger hemolytic anemia, a condition where red blood cells break apart faster than the body can replace them.
Children face the greatest risk from ingestion. Mothballs look like candy or marbles, and young children are naturally inclined to put them in their mouths. The EPA has flagged the widespread sale of illegal mothball products as a particular concern because of this risk to kids. While small accidental tastes in children are usually not life-threatening, even partial ingestion of a naphthalene mothball warrants immediate medical attention.
When Breathing Fumes Becomes Harmful
Inhalation is the more common exposure route for adults, and it’s the one most people underestimate. OSHA sets the workplace safety limit for naphthalene at 10 parts per million averaged over an eight-hour shift. That’s a ceiling for healthy adults in industrial settings with monitoring, not a number that accounts for children, elderly people, or continuous home exposure.
In a sealed closet or storage bin (the intended use), mothball fumes stay contained. The problems start when people scatter mothballs in attics, crawl spaces, basements, or rooms where the gas isn’t trapped. In these spaces, naphthalene vapor accumulates in the air you breathe. Symptoms of excessive inhalation include headaches, nausea, dizziness, and fatigue. Prolonged exposure over days or weeks can lead to the same red blood cell destruction seen with ingestion, causing dark-colored urine, pale skin, and shortness of breath.
If you can smell mothballs strongly in a living area, you’re being exposed at levels worth taking seriously. The characteristic mothball odor becomes detectable well below the OSHA limit, so a faint smell from a closed container is expected, but a room that reeks of mothballs indicates concentrations that shouldn’t be inhaled for extended periods.
Cancer Risk From Long-Term Exposure
Naphthalene is classified by the EPA as a possible human carcinogen, based on evidence of respiratory tumors in animal studies. The EPA has noted suggestive evidence linking inhaled naphthalene to nasal cancer, and the agency has specifically cited this concern when warning against illegal mothball products. The cancer risk applies primarily to chronic, repeated exposure rather than a single brief encounter, but it’s another reason to avoid using mothballs in open or living spaces.
People With G6PD Deficiency Face Extra Risk
G6PD deficiency is an inherited condition that affects how red blood cells handle oxidative stress. It’s most common in people of African, Mediterranean, Middle Eastern, and Southeast Asian descent. People with this condition are far more vulnerable to naphthalene. Their red blood cells are more susceptible to breaking apart when exposed, and the amount needed to trigger a dangerous reaction is roughly one-tenth of what would affect a person without the deficiency.
The tricky part is that many people don’t know they have G6PD deficiency until something triggers a reaction. If anyone in your household develops dark urine, yellowing skin, or unusual fatigue after mothball exposure, that combination of symptoms suggests hemolytic anemia and needs urgent medical evaluation.
Risks to Dogs and Cats
Pets are vulnerable to mothball poisoning through ingestion, inhalation, and even skin contact. Cats are suspected to be more sensitive than dogs or other household animals. A dog that chews on or swallows a mothball will typically show vomiting, loss of appetite, and abdominal pain first. With larger exposures to naphthalene, pets can develop anemia, difficulty breathing, pale gums, and in rare cases, tremors or seizures.
Paradichlorobenzene mothballs cause similar digestive symptoms in pets, along with lethargy and trembling. Repeated ingestion of paradichlorobenzene can lead to liver and kidney damage over time. Camphor-based mothballs, though less common, are the most dangerous to animals, primarily causing neurological symptoms including seizures and altered mental state.
If you use mothballs at all, they need to be in a sealed container that pets cannot access. Mothballs placed loosely in closets, under furniture, or in open areas are a poisoning risk every time a curious pet investigates.
How to Reduce Your Risk
The simplest rule: mothballs belong only in airtight containers with clothing or fabrics, exactly as the product label directs. Never use them as general pest repellents in gardens, attics, crawl spaces, car interiors, or anywhere that isn’t sealed. This isn’t just a safety recommendation; using mothballs in ways not described on the label violates federal pesticide law.
If you’ve been using mothballs in open spaces, ventilate the area thoroughly by opening windows and running fans. Naphthalene doesn’t break down quickly indoors, so fabrics and surfaces in a room with heavy mothball use can continue releasing fumes for weeks after the mothballs themselves are removed. Washing clothing that smells of mothballs before wearing it reduces skin contact with residual chemical.
For people who want moth protection without the chemical exposure, cedar blocks, lavender sachets, and simply keeping clothes clean before storage (moths are attracted to food residue and body oils on fabric) are effective alternatives that carry none of the toxicity concerns.