Derived from the chrysanthemum flower, the botanical extract pyrethrum is the source of pyrethrins--active ingredients in many mosquito coils, mosquito foggers, flea and tick sprays and human lice treatments. According to the U.S. Environmental Protection Agency, (EPA) over 3,500 registered pyrethrin products are hazardous to exposed persons if used improperly. Ingestion causes the most severe reactions, but inhalation and skin exposure could also create unpleasant symptoms in sensitive individuals.
Ingestion Reactions
For humans and other mammals, pyrethrin presents very little risk and is one of the least harmful insecticides. According to Cornell's Organic Resource Guide, an oral dose of 750 mg per kg of body weight could be fatal to children. One thousand mg per kg of weight could be lethal to adults. Pyrethrin-laced incense, spray or fog presents very little hazard and is approved for use in food preparation areas as long as food is either removed or covered.
Inhalation
When using foggers indoors, leave the closed room for the recommended period of time listed on the label. The EPA warns against using more than one fogger and recommends airing out the room after the fogger completes its treatment. Breathing high concentrations of pyrethrin fog could cause respiratory distress including wheezing, coughing and both chest and sinus pain. Use mosquito coils with proper ventilation and not in confined spaces.
Dermal Problems
Pyrethrin applications in ointment form treat common skin parasites such as scabies and head lice. When used properly, no harmful side effects should present, but if applications are combined with other skin ointments or are covered by bandages, the effects intensify. Sensitive patients might experience itching, skin rashes and possibly blister outbreaks. Don't apply pyrethrin to the eyes, the inside of the nose, or the mouth.
Effects on Wildlife
Once widely used in agriculture, pyrethrin powder now finds a place in organic gardens since the natural product kills most harmful garden insects. Pyrethrin breaks down quickly when exposed to sunlight, so residual effects fade rapidly. However, this potent nerve poison also kills beneficial insects like honeybees. In the soil, pyrethrins remains active for about 12 days and may contaminate nearby bodies of water if over-applied. Pyrethrin runoff could fatally poison aquatic life including fish, tadpoles and many invertebrates.
Long-term Effects
The National Pesticide Information Center states that no long-term studies or surveys of pyrethrin exposure--either accidental or work-related--show any carcinogenic effects on humans. In animal studies, test subjects fed large daily doses of pyrethrin for two years did show an increase in benign tumors and skin lesions. The U.S. EPA's Health Effects Division Carcinogenicity Peer Review Committee concluded that test data indicated carcinogenic effects in animals. Animals severely poisoned by pyrethrin often recover quickly even without treatment.
