Mosquitoes can be avoided by covering up exposed skin, or staying indoors when the bugs are most active, experts say. (Associated Press)

DEET, the most common chemical ingredient in insect repellents, could be harmful to the central nervous system, new research suggests.

A report on the subject issued by researchers in France, in both Montpellier and Angers, was published on Aug. 5.

"We've found that DEET is not simply a behaviour-modifying chemical but also inhibits the activity of a key central nervous system enzyme, acetycholinesterase, in both insects and mammals," said Vincent Corbeil, of the Institut de Recherche pour le Développement in Montpellier.

DEET — also known by its full name N, N-diethyl-methyl-meta-toluamide — has proven effective since its discovery in 1953 at warding off insects, including mosquitoes.

Used with insecticides

It does not kill bugs, but its vapours discourage them from landing or climbing on people. As well, the higher the DEET concentration in a repellent formula, the longer it provides protection. DEET is commonly used with insecticides, also.

About 200 million people use DEET every year, and it's estimated that more than eight billion doses have been applied over the past 50 years, according to the journal BMC Biology.

"The findings question the safety of DEET, particularly in combination with other chemicals, and they highlight the importance of a multidisciplinary approach to the development of safer insect repellents for use in public health," the French researchers wrote.

SC Johnson, the company that manufactures the popular insect repellent OFF!, issued a statement saying people can use its products with confidence. It said product directions should be carefully followed.

Those directions include using just enough of the product to cover exposed skin, and avoiding over-application.

West Nile concerns

With many people aware of the dangers of the West Nile virus — and with federal and provincial agencies monitoring birds and mosquitoes — this latest French research is raising new questions about how much repellent should be used at any given time.

"What I usually tell people is that for younger children and babies, it's best to keep them away from insects in the first place," Dr. Carol Leet, a pediatrician in Brampton, Ont., told CBC News.

"Try to cover the children as much as possible. Probably the most effective way is to be covered," Leet said.

If you are using insect repellents, Leet said to keep the spray away from the face and mouth and be aware of the potency of some products.

"Some of these ones for adults have high concentrations of DEET, so make sure you have one specifically for children," she said.

Health Canada says prolonged use of any registered product containing DEET should be avoided in children under the age of 12. It recommends:

• For adults and children over 12 years of age, use a product with up to 30 per cent concentration of DEET. For children aged two to 12, use a product with up to 10 per cent concentration and apply it up to three times daily.
• For children aged six months to two years, use a product with up to 10 per cent concentration and apply it no more than once daily.
• For infants under six months of age, do not use personal insect repellents containing DEET. Instead, use a mosquito net when the child is outdoors in a crib, playpen or stroller.

Leet also says it's a good idea to mindful of the times of day when bugs are mostly likely to bite.

Whether you are concerned about adults or children, it's best, she said, to "keep away in the early morning and evening hours when the mosquitoes are liable to be out."