In tropical countries, it's the time of year when insects and pests seem to be everywhere. They bring diseases that could irritate or kill. Children are especially susceptible. They love to play outdoors without mind the buzzing creatures. Sometimes, they even enjoy the company because of the sound and the insect's acrobatics in the air.

One common practice, especially where children are concerned is to use an insect repellant. The traditional way is to use smoke to ward off these so-called pests. Some families would put fire to certain leaves and twigs from plants that emit a certain odor unacceptable to mosquitoes when burned. This is the precursor of the fumigation method where certain chemicals are sprayed into an area releasing fumes that carry smells that repel the mosquitoes.

For indoor use, the katol or mosquito coil was developed. This (originally) green coil is burned like a cigarette. The smoke that is released also repels the mosquitoes. Normally, the katol is used in the bedroom and is designed to last for the duration of the user's sleep or around eight hours .. Like cigarette, it leaves ashes that have to be swept up in the morning and disposed.

A more modern approach is to use lotions. These are formulations sprayed or rubbed onto the skin. Mosquitoes will not bite the person wearing the lotion because of the uninviting smell it detects as it approaches. A common ingredient in these lotions is a chemical called DEET.

DEET is short for N, N-diethyl-meta-toluamide. It was originally developed by the United States Army after World War 2 to be used in jungle warfare. It was used in Vietnam and Southeast Asia. It released for civil use in 1957.

In 1998, the US Environmental Protection Agency released a Registration Eligibility Decision stating that as long as consumers follow label directions and take proper precautions, “DEET insect repellents will generally not cause unreasonable risks to humans or the environment.” The document contains specifications for labeling including statements like; do not use under clothing, use just enough repellant to cover exposed skin or clothing, avoid over application of this product, after returning indoors wash treated skin with soap and water, and wash treated clothing before reusing. The document also specifics that statements about products being child-safe be removed from the labels.

Studies at Cornell University showed that employees of the Everglades National Park in Florida who were more exposed to the pesticide than co-workers were more likely to experience insomnia, mood disorders and impaired cognitive function. The US EPA document also acknowledged that there about 40 cases of seizures that could have been associated with DEET exposure, including 4 deaths.

Recent studies made by research teams led by Vincent Corbel from the Institut de Recherche pour le Développement in Montpellier, and Bruno Lapied from the University of Angers, France demonstrated that DEET inhibits the activity of a central nervous enzyme called acetylcholinesterase not only in insects but also in mammals. This could lead to neuromacular paralysis which could cause death by asphyxiation. DEET is often combined with carbamates and other acetylcholinesterase inhibitors producing a more potent mosquito repellant but a more toxic chemical as well.

DEET has also shown negative effects in the aquatic environment. It has been found to be toxic to coldwater fishes like rainbow trout and tilapia. The chemical is also a toxin for some species of fresh water zooplankton. In 1991, it was found in concentrations as high as 201 ng / L in the Mississippi River.

There are alternatives to DEET although these have not been proven to be as effective. Essential oils such as citronella do not produce the enzyme inhibiting effect of the synthesized repellant. Also, the US EPA monitors citronella as a biopesticide with a nontoxic mode of action. It is one ingredient that a parent can look for when shopping for an insect repellent, especially if it will be used on and around children.