Insect Repellents
Revised 12/2009
DEET (N, N-diethyl-M-toluamide) is the most predominately used insect repellent in the United States. DEET can be safely used to repel biting and disease-carrying pests such as mosquitoes, black flies, fleas and ticks. In addition to DEET, the Centers for Disease Control (CDC) also considers the following Environmental Protection Agency (EPA) registered products effective in providing insect repellent activity: picaridin, oil of lemon eucalyptus or PMD (p-Mentane-3,8-diol) and IR3535.
These insect repellents pose no significant health risks when used properly. Greater insect repellent concentrations provide a longer duration of protection. For example, one study showed that a product containing 23.8% DEET provided an average of 5 hours of protection from mosquito bites; a product containing 20% DEET provided almost 4 hours of protection; a product with 6.65% DEET provided almost 2 hours of protection; and products with 4.75% DEET were able to provide roughly 1 and a half hours of protection. The effectiveness of DEET does not increase at concentrations >50%. .
Picaridin is probably the most effective of the DEET alternatives. Oil of lemon eucalyptus and PMD (the chemically synthesized version of oil of lemon eucalyptus) provide similar repellent activity to low concentrations of DEET. In one study, IR 3535 provided a short duration of action of protection against mosquitos (22.9 minutes).
These products may be applied to skin, clothing, tents, bedrolls and screens. DEET and other insect repellents, which are recommended for humans, are not approved for veterinary use (largely because animals tend to ingest them by licking.) Talk with your veterinarian for advice about the appropriate product for use on your pet.
Although EPA recognized insect repellants pose no significant health risks when used properly, a few simple guidelines should be followed:
• The American Academy of Pediatrics (AAP) Committee on Environmental Health recommends that a maximum DEET concentration of 30% be used on infants and children
• Parents should choose the type and concentration of repellent to be used by taking into account the amount of time that a child will be outdoors, exposure to mosquitoes, and the risk of mosquito-transmitted disease in the area.
• DEET insect repellents should not be used on infants under 2 months of age
• Oil of eucalyptus insect repellent labeling states that it should not be used in children less than 3 years of age.
• Do not allow young children to apply the product themselves
• Do not apply to the hands of small children
• Avoid wounds, scratches, irritated skin and the areas around the eyes and mouth when applying
• Do not use under clothing.
• Use just enough repellant to cover exposed skin and/or clothing: avoid over saturation.
• Cleanse treated skin with soap and water after returning indoors.
• Wash treated clothing before next use.
• Do not spray in enclosed areas.
• To apply to face, spray or rub on hands first. Then rub on face. Do not spray directly into the face.
• Do not use insect repellent and sunscreen combination products. Sunscreens often require repeated application, which could lead to overexposure to the insect repellent.
Other than the routine precautions noted earlier, the EPA does not recommend any additional precautions for using registered repellents on pregnant or lactating women.
Insect Repellent Toxicity
DEET
DEET has a very rapid absorption. Ingestion of enough DEET may result in severe symptoms within 30 minutes. Peak plasma concentration is within 1 hour. Dermally, 50% of each topically applied dose of DEET is absorbed within 6 hours. DEET is metabolized by oxidative enzymes in the liver. DEET is rapidly eliminated mainly in the urine and to a lesser extent in the feces.
DEET is primarily toxic to the CNS, although the mechanism of action is unknown. Ingestion in children of 25ml of a 50% DEET solution has resulted in severe toxicity. In adults, ingestion 50ml of 100% DEET solution has resulted in severe toxicity. Clinical effects include:
CV- Hypotension and rarely bradycardia
CNS – Confusion, ataxia, hypertonicity, drowsiness and seizures
GI – Abdominal pain, nausea and vomiting
Dermatologic – Rash and contact urticaria
Psychiatric – Acute paranoid psychosis from repeated dermal applications
Reproductive – Non-teratogenic
For a clinically significant DEET ingestion, the benefits of activated charcoal should be weighed against the possibility of rapid onset seizures. Seizures are managed with benzodiazepines. If inhaled, move patient from exposure environment to fresh air. Monitor for respiratory distress. For eye exposures, remove contact lenses (if applicable) and irrigate eyes with copious amounts of room temperature normal saline or water for at least 15 minutes.
Other insect repellents
EPA studies have found picaridin to have low acute oral, dermal, and inhalational toxicity. Picaridin is classified as practically non-toxic for acute inhalational toxicity and primary dermal irritation. Picaridin is classified as slightly toxic for acute oral, acute dermal, and primary eye irritation.
Dermal use oil of lemon eucalyptus and PMD is unlikely to cause toxicity. Primary eye irritation may occur. In one study of 9 patients who ingested eucalyptus oil, those children and adults who ingested less than a swallow by history developed few, if any, symptoms. Those who ingested 5 mL or more developed gastrointestinal and sometimes central nervous system effects. Treatment is symptomatic and supportive.
IR 3535 has been used as an insect repellent overseas since 1998. There have been no reports of serious toxicity.
