Mothballs (Naphthalene & Paradichlorobenzene)

Mothballs are small pesticide blocks made almost entirely of one chemical — usually naphthalene or paradichlorobenzene (PDB). They're a solid, but they slowly turn straight into a vapour without melting first, which is why a jar of them gives off that strong, lasting smell. According to the US National Pesticide Information Center, when you can smell mothballs, you are actually breathing in the pesticide. The same chemicals also turn up in solid 'deodoriser' blocks for closets, bins, and toilets.

The whole point of a mothball is that its vapour fills an enclosed space and repels or kills clothes moths and their larvae, which feed on wool and natural fibres. The same heavy, lingering smell gets reused to mask odours, which is why paradichlorobenzene shows up in toilet and bin deodoriser blocks. They're cheap and long-lasting. The catch is that the very property that makes them work — constant vapour — is also what you end up breathing.

Look for 'naphthalene' or 'paradichlorobenzene' (also written 1,4-dichlorobenzene, para-dichlorobenzene, or PDB) in the active-ingredient line. Product names include moth balls, moth flakes, moth crystals, moth cakes, and old terms like white tar or tar camphor. Solid bathroom and closet blocks may just say 'deodoriser' or 'air freshener,' so check the ingredients rather than trusting the front label.

Closets, wardrobes, and storage boxes where clothes, blankets, or fur are kept, plus trunks of stored seasonal items. Paradichlorobenzene versions also appear as solid deodoriser blocks in toilets, urinals, and bins. The smell, and the chemical, can soak into stored fabrics, so a blanket or a bag of hand-me-downs can carry it long after the mothballs are gone.

Mainly by breathing the vapour, which builds up most in small, poorly ventilated spaces like a closet or a bathroom. It can also be absorbed from skin contact with treated clothing or blankets. The most dangerous route is swallowing: a single mothball can look like a sweet to a small child, and the NPIC notes one mothball can cause serious harm if eaten by a small child.

Naphthalene and PDB can cross the placenta, so reducing exposure during pregnancy is sensible. A US pregnancy-cohort analysis (the ECHO PATHWAYS study) found a small association between higher maternal levels of a naphthalene breakdown product and slightly shorter gestation and lower birth weight, though many things affect those outcomes and this doesn't prove cause. There's also a practical concern at the very end of pregnancy: a baby born with G6PD deficiency can be especially sensitive to naphthalene in the days after birth.

There isn't strong human evidence that ordinary household mothball use specifically harms men's fertility, and the main concerns here aren't sex-specific. Most of what's known about reproductive effects comes from high-dose animal studies, not typical home exposure. The bigger, well-documented risks — red-blood-cell damage and breathing irritation — apply to men and women alike.

This is the group of greatest concern. Hospitals have reported many cases of haemolytic anaemia — where red blood cells break apart — in infants and children who swallowed naphthalene mothballs or were in close contact with clothing and blankets stored in them. The risk is highest in children with G6PD deficiency, an inherited trait that's common in some Mediterranean, African, and South and East Asian backgrounds, where even modest exposure can trigger a serious haemolytic crisis. Because of this, the safest move is to keep mothballs out of any home with young children entirely.

There isn't strong evidence that healthy older adults react very differently from other adults to everyday exposure. The same general effects apply — breathing irritation, headaches, dizziness, and red-blood-cell damage at higher exposure. Anyone of any age with G6PD deficiency is more sensitive, so that trait matters more than age itself.

The clearest, best-documented effect is on red blood cells: the US EPA's hazard summary states that short-term naphthalene exposure may cause cataracts and haemolytic anaemia in people, and case reports link mothball ingestion to severe haemolysis in G6PD-deficient children. On cancer, the EPA classifies both naphthalene and paradichlorobenzene as Group C, possible human carcinogens, and the International Agency for Research on Cancer lists both as possibly carcinogenic to humans (Group 2B) — 'possible,' not proven. Both substances are recognised pesticides regulated by the EPA, which is why labels strictly limit how they can be used.

For a healthy adult, a brief whiff from a stored coat is a low-level concern. The risk rises sharply with enclosed, ongoing exposure — mothballs left open in a bedroom closet or a small bathroom — and is highest for infants, young children, and anyone with G6PD deficiency, where even indirect contact through stored bedding has caused real harm. Because safer storage works just as well, the simplest read is: there's little reason to accept the exposure at all.

Cedar blocks, balls, or a cedar-lined chest repel moths with a scent that's far less concerning — refresh it occasionally by sanding lightly. Even simpler: store off-season clothes in sealed airtight bins or vacuum bags so moths can't reach them, and wash or dry-clean wool before storing, since moths are drawn to body oils and food residue, not clean fabric. For bathroom odours, ventilation and ordinary cleaning replace solid PDB blocks.

Easy. Mothballs are an optional product with well-established replacements that cost about the same. The main effort is checking the spots they hide — closets, storage trunks, and bathroom cupboards — and switching to cedar or sealed storage. If you do use any mothball product, it must be used only as directed on the label, sealed inside an airtight container, never loose in living space.

Walk through your closets, storage boxes, and bathroom cupboards and pull out any mothballs, moth flakes, or solid deodoriser blocks. Bag them to dispose of according to the label, then open a window or run a fan to air the space out. If you have stored baby clothes or hand-me-downs that smell of mothballs, wash and air them before anyone wears them.

Mothballs are a clear, low-effort win. The vapour you can smell is the pesticide, the strongest concern is red-blood-cell damage in babies and children, and the alternatives — cedar and sealed airtight storage — work just as well. This isn't about fear: it's about using these products only as the label directs and keeping them out of the rooms where your family breathes, sleeps, and plays.

ATSDR's ToxFAQs and the EPA hazard summaries cover naphthalene and paradichlorobenzene, and the National Pesticide Information Center (NPIC) has plain-language pages on mothballs and safer alternatives. For the science on G6PD and pregnancy, peer-reviewed case reports and the ECHO PATHWAYS pregnancy-cohort work are good starting points. See References below.