Insect Repellents

Natural & Botanical Repellents

The Annals of Internal Medicine (June 98) reports:

Plants whose essential oils have been reported to have repellent activity include citronella*, cedar, verbena, pennyroyal, geranium, lavender, pine, cinnamon, rosemary, basil, thyme, allspice, garlic, and peppermint. Unlike synthetic insect repellents, plant-derived repellents have been relatively poorly studied. When tested, most of these essential oils tended to give short-lasting protection, usually less than 2 hours.

*Citronella is registered with U.S. EPA as an insect repellent. Studies show that citronella can be an effective repellent, but it provides shorter complete protection time than most DEET-based products.

While all of the natural repellents mentioned above provide shorter coverage, they also provide safer coverage. Moreover, they may be ideal for shorter evening chores like walking the dog, grilling, or taking out trash and recycleables.

How To Use DEET Products Safely

Consumers can reduce their own risks when using DEET by reading and following products labels. Statements on all DEET product labels will be revised to include the following directions:

Read and follow all directions and precautions on this product label.
Do not apply over cuts, wounds, or irritated skin.
Do not apply to hands or near eyes and mouth of young children.
NEVER spray repellants directly on the skin of children under three years old or on the hands of children of any age who may put their hands in their mouths.
Do not allow young children to apply this product.
Use just enough repellent to cover exposed skin and/or clothing.
Do not use under clothing.
Avoid over-application of this product.
After returning indoors, wash treated skin with soap and water.
It is best to spray repellents on your clothes BEFORE you put them on.
Wash treated clothing before wearing it again.
Use of this product may cause skin reactions in rare cases. The following additional statements will appear on the labels of all aerosol and pump spray formulation labels:
Do not spray in enclosed areas.
To apply to face, spray on hands first and then rub on face.
Do not spray directly onto face.
Repellents with DEET can be applied to clothing , window screens, tents, or sleeping bags. If DEET-treated garments are stored in a plastic bag between
wearings, the repellent effect can last for many weeks

Toxicology of DEET (DIETHYLTOLUAMIDE)

The following information is taken from the U.S. EPA Recognition and Management of Pesticide Poisonings, Fifth Edition, pp 80-83.

This chemical is a widely-used liquid insect repellent, suitable for application to skin or to fabrics. It comes in a wide range of concentrations from 5% (Off!, Skintastic for Kids) to 100% (Muskol). Compared to the widespread use of the product, there are relatively few cases of toxicity. However, if used improperly, ingested, or a very high
concentration is used on children, especially repeatedly over large skin surfaces, the potential for severe toxicity exists. DEET is formulated with ethyl or isopropyl alcohol.

For many years, diethyltoluamide has been effective and generally well tolerated as an insect repellent applied to human skin, although tingling, mild irritation, and sometimes desquamation have followed repeated application. In some cases, DEET has caused contact dermatitis and excerbation of pre-existing skin disease. It is very irritating to the eyes, but not corrosive.

Serious adverse effects have occurred when used under tropical condition, when it was applied to areas of skin that were occluded during sleep (mainly the antecubital and popliteal fossae). Under these conditions, the skin became red and tender, then exhibited blistering and erosion, leaving painful weeping denuded areas that were slow to heal. Severe scarring occasionally resulted from some of these severe reactions. DEET is efficiently absorbed across the skin and by the gut. Blood concentrations of about 0.3 mg/dL have been reported several hours after dermal application in the prescribed fashion.' The amount absorbed increases as the concentration of DEET rises. In addition, many commercial formulations are prepared with ethanol as a solvent, which further increases absorption. Toxic encephalopathic reactions have apparently occurred in rare instances following dermal application, mainly in children who were intensively treated. The more frequent cause of systemic toxicity has been ingestion: deliberate in adults and accidental in young children.

Manifestations of toxic encephalopathy have been behavioral disorders including headache, restlessness, irritability, ataxia, rapid loss of consciousness, hypotension, and seizures. Some cases have shown flaccid paralysis and areflexia. Deaths have occurred following very large doses. Blood levels of DEET found in fatal systemic poisonings have ranged from 168 to 240 mg per liter.

Interpretation of DEET toxicity in some fatal cases has been complicated by effects of simultaneously ingested ethanol, tranquilizers, and other drugs. One well-documented case of anaphylactic reaction to DEET has been reported. One fatal case of encephalopathy in a child heterozygous for ornithine carbamoyl transferase deficiency resembled Reyes syndrome, but the postmortem appearance of the liver was not characteristic of the syndrome.

Discretion should be exercised in recommending DEET for persons who have acne, psoriasis, an atopic predisposition, or other chronic skin condition. It should not be applied to any skin area that is likely to be opposed to another skin surface for a significant period of time (antecubital and popliteal fossae, inguinal areas).

Great caution should be exercised in using DEET on children. Avoid repeated application day after day. Applications should be limited to exposed areas of skin, using as little repellent as possible and washing off after use. Do not apply to eyes and mouth and, with young children, do not apply to their hands. Low concentrations (10% or below) are effective and may be preferred in most situations. There are formulations labeled for children that have concentrations of 5 to 6.5% DEET. If continuous repellent protection is necessary, DEET should be alternated with a repellent having another active ingredient. If headache or any kind of emotional or behavioral change occurs, use of DEET should be discontinued immediately.

Confirmation of Poisoning

Methods exist for measurement of DEET in blood and tissues and of metabolites in urine, but these are not widely available.

Treatment

1. Skin decontamination. Wash skin with soap and water. Eye contamination should be removed by prolonged flushing of the eye with copious amounts of clean water or saline. If irritation persists, specialized medical treatment should be obtained. Topical steroids and oral antihistamines have been used for severe skin reactions that occasionally follow application of DEET.

2. Gastrointestinal decontamination. If a substantial amount of DEET has been ingested within an hour of treatment, gastrointestinal decontamination should be considered. Induced emesis is usually considered contraindicated in these poisonings due to the rapid onset of seizures.

3. Seizures. Treatment is primarily supportive, with control of seizures by
anticonvulsants. Persons surviving poisoning by ingestion of DEET have usually recovered within 36 hours or less.

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