The scalp is one of the most absorbent parts of the body. Products applied to the scalp go directly to the blood, without being filtered in any way. Pesticide based lice shampoos contain ingredients which are known or suspected to cause cancer, affect the nervous system, and have other harmful effects. They can trigger asthma or allergic responses. Children, especially children with asthma and allergies, are more vulnerable than adults to these chemicals.

The most common pesticides used in lice treatment in Nova Scotia are permethrin, pyrethrum, and piperyl butoxide. Lindane based shampoos are still approved for use in Canada, and in most provinces are available “behind the counter.” In the US, malathion based shampoos are still common.

Permethrin - A pyrethroid insecticide, permethrin is a synthetic version of an extract from the chrysanthemum. Exposure to pyrethroids has resulted in contact dermatitis and asthma-like reactions. Children with a history of allergies or asthma are particularly sensitive. Permethrin is a suspected human carcinogen and neurotoxin which has been reported to cause temporary nervous disorders in the face and hands. It is also a suspected reproductive toxicant and endocrine toxicant.

Pyrethrum - This is a natural insecticide made from chrysanthemums. Pyrethrum insecticide formulations often contain piperonyl butoxide, a synthetic chemical that increases the potency of pyrethrum. Pyrethrum can trigger allergic responses like skin rashes, hives and asthma. It is a suspected carcinogen, immunotoxicant and reproductive toxicant. Piperonyl butoxide is a suspected carcinogen, neurotoxicant and respiratory toxicant.

Lindane - Lindane was once the lice treatment of choice. It is now recognized as highly toxic, although lindane based lice control products are still approved for use in Canada. Lindane is an organochloride insecticide in the same chemical class as DDT. A nerve poison, lindane is readily absorbed through the skin and is classed as a known cancer-causing chemical in California where it is banned. Documented health effects of exposure to lindane include hormone disruption, dizziness, seizures, nervous system damage, immune system damage and birth defects. Lindane, also an agricultural pesticide, has been found in breast milk and blood samples throughout the world and is banned in at least 14 countries.

Seizures, behavioral changes, attention deficit disorders, brain injury, skin diseases, and even death have been reported to the United States-based National Pediculosis Association's registry by people who have used chemical treatments to get rid of head lice or scabies.

Toxicity information from www.scorecard.org.