Mothballs contain chemicals that emit fumes as the balls break down. These fumes are actually caused by an insecticide, designed to kill moths when the mothballs are packed with clothing or fabrics within an airtight container. The insecticidal chemicals -- naphthalene or paradichlorobenzene -- are toxic and potentially harmful to humans, pets and plants.
Harm to Humans
While using mothballs as intended -- placing them in an airtight container -- may elicit no noticeable health effects, exposure to their fumes or accidental ingestion may be cause for concern. Naphthalene, found in some mothballs, is considered potentially carcinogenic to humans. Exposure to mothball vapors may cause dizziness, headaches, nausea and vomiting. Eating mothballs can cause convulsions, coma and damage to kidneys, liver and brain. Wash your hands thoroughly after touching mothballs or fabrics that smell of mothballs.
Problems for Pets
Mothballs are harmful to both cats and dogs -- and not just when the pets ingest them. The chemicals in mothballs may affect your pet through skin contact or through inhalation of fumes, as well as through the stomach and intestines. Old-fashioned naphthalene mothballs are more toxic than the newer paradichlorobenzene varieties; both types are harmful to pets. Beside cats and dogs, the chemicals in mothballs are also harmful to other mammals such as rodents. Mothballs may cause pet seizures, coma, death, tremors, diarrhea and vomiting. If your pet's breath smells of mothballs, or you suspect it may have come into contact with them, contact your veterinarian or call the Pet Poison Control Helpline.
Mothballs are regulated by the Environmental Protective Agency for use as a pesticide within an enclosed or airtight environment -- they are not allowed nor designed to repel pests within gardens or potted plants because the mothballs release harmful chemicals into both the soil and air as they break down. Plants absorb chemicals within nearby soil, so any edible plants grown with mothballs nearby may contain toxins. Strong concentrations of mothball chemicals may inhibit plant growth or harm the plants.
Instead of using toxins to control moths on clothing and textiles, store these materials in an airtight container where moths are unable to reach them. If you're concerned about items stored for long periods of time in a non-airtight environment such as a closet, shake the clothing or textiles out on a monthly basis to release any hidden moth larvae, or place the items in a dryer or hang them outside on a sunny day to remove larvae. Shake the clothes out before storing them again to remove any clinging larvae.