New Study Finds Insecticidal Lice Shampoos Contaminate Children’s Bodies

(Beyond Pesticides, February 23, 2009)

Permethrin and lindane metabolites are found in children who use lice shampoos containing the insecticides, according to researchers affiliated with the Centers for Disease Control and Prevention. The study, “Pesticide exposure resulting from treatment of lice infestations in school-aged children in Georgia,” published in the February issue of the journal Environment International, is the first to measure children’s exposure to chemical lice treatments.

The researchers collected baseline urine samples from 78 enrolled children between the ages of six to ten years of age. About one-third of those children were diagnosed with head lice and subsequently treated with at least one over-the-counter permethrin lice treatment, a prescription lindane treatment, or both. Within seven days of the insecticide application, urine samples were again collected. The permethrin exposed children had significantly higher urinary pyrethroid metabolite levels in their post-exposure urine samples. Lindane metabolites were also elevated in urine samples after treatment. Interestingly, the study states, “Exposed participants appeared to have higher pre-exposure metabolite levels likely from multiple treatments before enrollment than unexposed participants.” Pentachlorophenol, a metabolite of lindane, was significantly higher in the urine of those children who used a lice treatment regardless of whether it was lindane-based. When looking at the children’s urinary pentachlorophenol and the three permethrin metabolite levels, the study authors unexpectedly found age-related differences. The middle age group of children, between the eight and eleven years old, had lower metabolite levels than the older or younger children. In addition, “For those participants whose urine samples were collected more than one day following exposure, a larger percentage of the pesticide metabolites would have been eliminated from the body before sample collection making it more difficult to ascertain if an exposure had occurred,” and thus possibly weakening the study results.

Permethrin is a possible human carcinogen and exposure is linked to possible endocrine disruption, immunotoxicity, neurotoxicity and reproductive effects. Exposure to synthetic pyrethroids such as permethrin has been reported to lead to headaches, dizziness, nausea, irritation, and skin sensations. Children are especially sensitive to the effects of permethrin and other synthetic pyrethroids. A study found that permethrin is almost five times more toxic to eight-day-old rats than to adult rats due to incomplete development of the enzymes that break down pyrethroids in the liver. Studies on newborn mice have shown that permethrin may inhibit neonatal brain development. Additionally, researchers have documented low-dose effects permethrin, doses below one-one thousandth of a lethal dose for a mouse, on those brain pathways involved in PD. The effects are consistent with a pre-Parkinsonsian condition, but not yet full-blown Parkinsonism.

Lindane has long been used in the treatment of head lice, yet is widely known for its neurotoxic properties, causing seizures, damage to the nervous system, and weakening of the immune system. It is also a probable carcinogen and endocrine disruptor. Lindane is particularly toxic and is also bioaccumulative. When used on people, lindane is regulated by the Food and Drug Administration (FDA). Despite the fact that it has been banned in 52 countries and restricted in over 30 more, the Food and Drug Administration (FDA) continues to allow its use in the U.S., albeit with a Public Health Advisory issued in 2003 that states, “Lindane should be used with caution in infants, children, the elderly, patients with skin conditions, and patients with low body weight (less than 110 lbs).” The last remaining agricultural uses of lindane were cancelled in 2006. It was banned in California in 2000 because of high levels of water contamination. Following the ban, water contamination drastically declined, and an increase in head lice cases was not reported.

Head lice affect an estimated 12 million people in the U.S. each year, and are rapidly becoming resistant to over-the-counter and prescription medications. According to researchers on alternative lice treatments, one method for eliminating head lice that will not lead to resistant strains of lice is the use of hot air, which desiccates the insects and eggs, thus killing them.