In humans, exposure to large amounts of naphthalene may damage or destroy red blood cells. This could cause the body to have too few red blood cells until it replaces the destroyed cells. Humans, particularly children, have developed this condition after ingesting mothballs or deodorant blocks containing naphthalene. Some of the symptoms of this condition are fatigue, lack of appetite, restlessness, and pale skin. Exposure to large amounts of naphthalene may also cause nausea, vomiting, diarrhea, blood in the urine, and jaundice (yellow coloration of the skin).
When the U.S. National Toxicology Program exposed male and female rats and mice to naphthalene vapors on weekdays for two years (1), male and female rats exhibited: clear evidence of carcinogenic activity, based on increased incidences of adenoma and neuroblastoma of the nose, female mice exhibited some evidence of carcinogenic activity, based on increased incidences of alveolar and bronchiolar adenomas of the lung, and male mice exhibited no evidence of carcinogenic activity.
The International Agency for Research on cancer (IARC) (2) classifies naphthalene as possibly carcinogenic to humans [Group 2B]. It also points out that acute exposure causes cataracts in humans, rats, rabbits, and mice and, that haemolytic anaemia, described above, can occur in children and infants after oral or inhalation exposure or after maternal exposure during pregnancy.
Over 400 million people have an inherited condition called glucose-6-phosphate dehydrogenase deficiency. For these people, exposure to naphthalene is harmful and may cause hemolytic anemia, which causes their erythrocytes to break down.
