Is It Bad to Smell Mothballs? The Health Risks

Smelling mothballs means you are inhaling chemicals that carry genuine health risks, especially with repeated or prolonged exposure. Mothballs are not inert room fresheners; they work by slowly turning from solid to gas, releasing either naphthalene or paradichlorobenzene into the air around them. Both substances are toxic to varying degrees, and the fumes are the delivery mechanism for every health concern associated with the product. A faint whiff in a closet is a lower-stakes encounter than living in a home saturated with the smell, but the science is clear that neither chemical is harmless to breathe.

What You Are Actually Breathing

Mothballs sold today contain one of two active ingredients. The older and more common formulation uses naphthalene, a polycyclic aromatic hydrocarbon derived from coal tar or petroleum. The alternative, paradichlorobenzene, is a chlorinated benzene compound that smells somewhat sweeter and dissolves more readily than naphthalene. A simple turpentine-dissolution test can distinguish the two: paradichlorobenzene dissolves far faster, with all paradichlorobenzene mothballs fully dissolving in 60 minutes while at least a quarter of the naphthalene remained intact under the same conditions.¹ That dissolution rate matters at home, too: both chemicals sublimate, meaning they skip the liquid phase and go straight from solid to gas. That gas is what you smell, and it fills whatever space the mothball sits in.

Most people assume the smell is merely unpleasant. In reality, it signals that volatile organic compounds are accumulating in the air you breathe. The concentration depends on how many mothballs you have, how enclosed the space is, and how long they have been sublimating. Mothballs used as intended, sealed inside airtight containers with clothing, produce far lower ambient levels than mothballs scattered in open closets, attics, or rooms.

Indoor Air Concentrations Can Climb Surprisingly High

Research measuring naphthalene levels inside homes has found that concentrations vary enormously depending on use patterns. One study reported a median indoor long-term naphthalene concentration of about 0.9 micrograms per cubic meter, but the distribution was heavily skewed toward the high end. Roughly 14% of homes exceeded 3 micrograms per cubic meter, which is the chronic reference concentration for non-cancer health effects. About 8% exceeded 10 micrograms per cubic meter, and some homes reached concentrations as high as 200 micrograms per cubic meter.² That top range is staggering, more than 60 times the reference level, and typically occurs in homes where mothballs are placed in open areas or used in large quantities well beyond label directions.

The gap between the median and those extreme readings is important for understanding your own risk. If your only contact with mothball smell is opening a cedar chest once a season, you are at the low end. If mothballs sit in open bowls around a poorly ventilated apartment, the air in that home can reach concentrations that are genuinely hazardous over time.

Short-Term Exposure and Acute Symptoms

The smell itself is a warning that you are inhaling a biologically active substance. Short-term inhalation of mothball fumes can cause headaches, nausea, dizziness, and irritation of the eyes, nose, and throat. These symptoms tend to appear quickly in poorly ventilated spaces and resolve once you move to fresh air. For most healthy adults, a brief encounter is more annoying than dangerous.

The more serious acute risk relates to hemolytic anemia, a condition in which red blood cells are destroyed faster than the body can replace them. Naphthalene is an oxidizing agent: once metabolized, it generates reactive molecules that damage the hemoglobin inside red blood cells. The body typically has antioxidant defenses to counterbalance this, but in large or sustained exposures, or in people with less robust defenses, the oxidative stress overwhelms the system. The result can include dark-colored urine, jaundice, fatigue, and in severe cases, kidney failure.³ Paradichlorobenzene can cause the same hemolytic response and can also trigger methemoglobinemia, where hemoglobin is altered so it cannot carry oxygen effectively.

People With G6PD Deficiency Face Much Greater Danger

Glucose-6-phosphate dehydrogenase deficiency, usually called G6PD deficiency, is one of the most common inherited enzyme disorders in the world. It affects an estimated 400 million people globally, with the highest prevalence in populations of African, Mediterranean, Middle Eastern, and Southeast Asian descent. People with G6PD deficiency have red blood cells that are unusually vulnerable to oxidative damage because they cannot generate enough of the protective molecule that normally shields those cells.

For someone with G6PD deficiency, even moderate exposure to naphthalene or paradichlorobenzene can trigger a hemolytic crisis. The gradual buildup of oxidizing radicals in a setting of restricted antioxidant availability leads to rapid destruction of red blood cells, causing severe anemia that may require blood transfusions.³ What makes this especially treacherous is that many people do not know they carry the deficiency until an exposure triggers a reaction. Children are particularly vulnerable: one case report described a toddler with undiagnosed G6PD deficiency who developed severe hemolytic anemia, methemoglobinemia, and multiple organ failure after mothball exposure.⁴

Newborns and Infants Are Especially Vulnerable

Babies face a dual problem: their metabolic systems are immature, and they cannot move away from contaminated air. Mothball vapor inhalation in the home has been documented as a cause of severe neonatal jaundice and a condition called kernicterus, in which bilirubin from destroyed red blood cells crosses into the brain and causes permanent neurological damage. In one report of seven male newborns of Chinese, Greek, and Italian origin who presented with severe hemolytic jaundice from G6PD deficiency, five of the seven cases were precipitated by inhalation of mothball vapors in the home. Kernicterus was evident upon admission in six of the infants and was fatal in four.⁵

These were not cases of deliberate ingestion. The babies were simply living in homes where mothballs were in use, and the ambient vapor was enough to trigger a crisis in infants with an underlying enzyme deficiency. Maternal ingestion of mothballs during pregnancy has also been linked to severe toxicity in the newborn, including hemolytic anemia requiring exchange transfusion, pulmonary hypertension, respiratory failure, and renal failure.⁶ The message for families with infants, especially those of ethnic backgrounds where G6PD deficiency is common, is unambiguous: mothballs should not be used in the home.

Cancer Risk From Chronic Naphthalene Exposure

The cancer question is where the evidence sits in a frustrating gray zone. Animal studies have consistently shown that chronic inhalation of naphthalene causes tumors. Two-year inhalation studies in rodents found increased rates of respiratory epithelial adenomas in males, olfactory epithelial neuroblastomas in both sexes, and various nonneoplastic nasal lesions.⁷ Separate bioassays in mice and rats also demonstrated lung and nasal cancers following inhalation exposure.⁸

What remains debated is how directly those animal findings translate to humans. The International Agency for Research on Cancer classifies naphthalene as “possibly carcinogenic to humans” (Group 2B), meaning there is limited evidence in humans but sufficient evidence in experimental animals. Epidemiological data from humans is thin, largely because it is hard to isolate mothball exposure from other sources of polycyclic aromatic hydrocarbons in occupational and residential settings. The animal evidence is strong enough that regulatory agencies treat chronic naphthalene exposure as a cancer concern, but the exact risk to someone with typical home-use exposure levels remains uncertain.

Liver and Kidney Damage From Paradichlorobenzene

While naphthalene gets most of the attention for blood-related toxicity and cancer, paradichlorobenzene carries its own distinct organ risks. Animal studies show that paradichlorobenzene exposure causes significant oxidative damage in the liver and kidneys. In mice treated with the chemical, markers of lipid peroxidation (a sign that cell membranes are being destroyed by reactive oxygen) increased markedly in both organs at higher doses, alongside changes in trace element levels that further indicate tissue injury.⁹ These effects suggest that chronic paradichlorobenzene exposure can quietly damage the organs responsible for detoxifying the body.

This is relevant because paradichlorobenzene mothballs are sometimes marketed as a “safer” alternative to naphthalene. In terms of acute hemolytic risk, paradichlorobenzene may be somewhat less potent. But the organ toxicity data makes it clear that “less toxic” is not “non-toxic,” and the liver and kidney effects accumulate with duration rather than requiring a single dramatic exposure event.

Neurological Effects From Chronic Paradichlorobenzene Exposure

One of the more alarming documented effects involves the brain. Chronic exposure to paradichlorobenzene has been linked to a condition called leucoencephalopathy, which is diffuse damage to the white matter of the brain. In one case, a patient with chronic paradichlorobenzene ingestion (from mothballs and toilet cakes) presented with altered mental status, difficulty walking, muscle rigidity, and characteristic skin rashes. Brain imaging revealed diffuse periventricular and white matter disease consistent with toxin-induced leucoencephalopathy.¹⁰

This kind of brain damage has been documented primarily in cases of deliberate ingestion or abuse (some people habitually sniff or eat mothballs), but the underlying mechanism, chronic buildup of a neurotoxic compound, should concern anyone with heavy long-term inhalation exposure as well. The fact that the diagnosis in the case above was initially missed until family members revealed the exposure pattern illustrates how easily mothball toxicity can go unrecognized. Clinicians may not think to ask about it, and patients or their families may not think to mention it.

Eye Damage and Cataract Formation

Naphthalene is a well-established cause of cataracts in laboratory animals. The mechanism involves naphthalene metabolites accumulating in the lens of the eye and triggering oxidative damage that clouds the lens over time. This finding is so reliable that naphthalene-induced cataracts are used as an experimental model for studying age-related cataracts in humans.¹¹ The parallel to human senile cataracts has been explored across multiple studies in both rats and rabbits.¹²

Whether typical residential mothball exposure produces enough naphthalene to contribute to cataract formation in people is not established with certainty. The doses used in animal research are far higher than what most people encounter. But the concern is real enough that it adds another reason to minimize unnecessary exposure, particularly for people already at elevated risk for eye disease.

Common Misconceptions About Mothball Safety

Several widely held beliefs about mothballs are wrong in ways that increase exposure risk:

They’re safe if you can tolerate the smell. Absence of immediate symptoms does not mean the chemicals are not accumulating in your body or damaging tissues. Chronic low-level exposure causes effects that build gradually over months or years.
They’re meant for open spaces. Product labels consistently direct users to place mothballs in sealed containers with clothing. Scattering them in attics, under houses, in gardens, or around rooms violates the labeled instructions and dramatically increases vapor concentrations. Using them to repel snakes, rodents, or insects in open areas is both ineffective and illegal in the United States under EPA regulations, since it constitutes use inconsistent with the label.
Paradichlorobenzene is the safe kind. While paradichlorobenzene may produce somewhat less severe acute hemolytic reactions than naphthalene, it carries its own risks of liver damage, kidney damage, and neurotoxicity. Switching from naphthalene to paradichlorobenzene mothballs is a lateral move, not a safety upgrade.
Only ingestion is dangerous. The case reports of neonatal kernicterus from mothball vapor in the home demonstrate that inhalation alone, without any ingestion, can cause severe and even fatal outcomes in susceptible individuals.

Safer Alternatives for Moth Protection

If your goal is protecting stored woolens and other natural fibers from moth damage, several options avoid the chemical risks entirely. Cedar blocks and cedar oil contain natural compounds that repel moths, though their effectiveness diminishes as the wood ages and the oils evaporate, meaning they need periodic sanding or refreshing with cedar oil. Lavender sachets are a traditional alternative that many people find pleasant rather than noxious. Pheromone traps designed for clothes moths can help monitor and reduce populations. And the single most effective moth prevention strategy requires no products at all: clean garments thoroughly before storing them, since moths are attracted to the oils and residues left by human wear, and store them in airtight bags or containers. A moth cannot eat what it cannot reach.

For people dealing with active moth infestations rather than prevention, freezing infested garments for several days kills moth larvae at all life stages. Dry cleaning accomplishes the same thing chemically. Neither approach leaves a toxic residue in your living space.

Why Mothball Misuse Is So Widespread

Part of the reason mothball exposure remains a public health issue is cultural. In many communities around the world, mothballs have been used for decades not just for their intended purpose but as general air fresheners, insect repellents, and even folk remedies. Some people place them in rooms, cars, or closets simply because the smell is associated with cleanliness. In some cultures, pregnant women have been known to ingest or heavily use mothballs based on traditional practices, which is how cases of neonatal toxicity from maternal exposure arise. The growing awareness of indoor environmental health risks associated with naphthalene, including contributions from mothball use, has led researchers to call for better public education and labeling.¹³

The disconnect between how mothballs are labeled and how they are actually used is the core of the problem. When used strictly according to directions, sealed inside airtight containers with clothing, the exposure risk is low for healthy adults. When used as open-air deodorizers or scattered around living spaces, they become a meaningful source of chronic chemical exposure in the home. The fact that they are sold over the counter and have been around for generations gives them an air of harmlessness they have not earned.