A mosquito repellent that includes a compound from tomatoes could prove safer and more effective than current chemicals.

Preventing mosquito bites is a key part of efforts to prevent the spread of diseases such as malaria and dengue fever, particularly among travellers to tropical countries.

Deet (N, N-diethyl-meta-toluamide), the active ingredient in the majority of repellent sprays and creams, has been linked with occasionally severe reactions.

The US Environmental Protection Agency no longer allows labels of products containing Deet to describe them as "safe for children".

It's found in tomatoes, it's natural, it can be obtained organically, it's safe and it's at least as effective as Deet

Dr Michael Roe, North Carolina State University

The discovery, by scientists at North Carolina State University, US, could produce a repellent which is less toxic.

The tomato plant has an innate ability to fend off attacks from insects.

Dr Michael Roe, Professor of Entomology at North Carolina, took an extract of the plant and tested it to see if it had specific effects on mosquitoes - which can carry the malaria parasite.

Some mosquitoes carry disease

They found it to be extremely effective not only against mosquitoes, but also against ticks, which are commonplace in many countries and can also carry disease.

In addition, the compound - labelled IBI-246 -is already used extensively in cosmetics, meaning that its toxicity has been well-tested.

The university has patented its use as an insect repellent, and a biotechnology firm is using it as the basis for new products.

Dr Roe said: "It's found in tomatoes, it's natural, it can be obtained organically, it's safe and it's at least as effective as Deet, all features that the public would want for a new-generation insect repellent.

"With the concern about West Nile virus and Lyme disease, spread by mosquitoes and ticks, respectively - in the US and with the threat of other diseases such as malaria outside the US, people need the personal protection of insect repellents."

On the way

Researchers are hopeful that a product containing the extract will be on the market by the end of the year.

Professor Chris Curtis, from the London School of Tropical Hygiene and Medicine, London, UK, said that Deet had, perhaps unfairly, received a bad press in the past.

He said: "There have been reports of adverse reactions, but when these are compared with the millions of applications of repellents containing Deet, it really does appear to be relatively safe.

"The only difficulty is that it can damage certain plastics if it comes into contact with them.

"We have tested a variety of products and found that all of them are effective, although not 100%, including one containing lemon and eucalyptus."