Mosquitoes are more than just pests that cause itchy welts. They carry killer diseases including malaria. Mosquitoes also transmit "break-bone fever", or dengue, and pass on parasitic "filarial" worms that can cause major swelling that requires amputation. Knowing what repellent best deters the little devils is vital because, as the Consumer Council states, they may feast on you. You might want to ponder alternatives including geranium oil extract and picaridin because the council is critical of the default chemical deterrent, Deet (short for N,N-diethyl-meta-toluamide). Common Deet side effects include rash and, what's worse, excessive exposure may even cause seizures, the council says. British bite protection expert Howard Carter also blasts Deet. The artificial repellent is a proven neurotoxin and unsafe for children, Carter says. He adds that French scientists who investigated Deet's toxicity found it to be behaviour modifying - it inhibits the activity of a key central nervous system enzyme [acetylcholinesterase] in both insects and mammals. "This raises serious questions about Deet's safety, particularly when combined with other chemicals," Carter says. Use Deet-free repellents containing pure citronella instead, he says. Health and beauty merchant Margot White, founder of thechoosychick.com who specialises in non-toxic products, agrees Deet must be avoided - and can be easily. "There are some great Deet-free alternatives to traditional bug repellents," White says. "The good news is that they don't overwhelm you with a plume of spray that makes you cough … and they actually work." A deterrent she recommends is Badger Balm Anti-Bug Shake & Spray, an organic and natural spray that repels mozzies with fragrant citronella, rosemary, and wintergreen essential oils. The spray, which contains no Deet, petroleum products, or synthetic chemicals, has been laboratory tested independently and is considered safe and effective for the family, White says. (See sidebar for other natural repellents.) There are Deet-free alternatives ... and they actually work margot White, founder of thechoosychick.com Citronella is a key component in the anti-mosquito crusade - a common component in mosquito coils - but doubt surrounds whether the product, derived from the leaves and stems of lemon grass, is safe and effective. According to the Consumer Council, citronella faces scrutiny thanks to a fragrant contaminant called methyl eugenol. Tests by vector-borne disease specialist Dr Robert Novak revealed that for citronella coils to be effective, you must remain in its smoky plume. When smoke from a citronella coil engulfed a human test participant's shin, the mosquitoes just detoured and bit their calf. Another reason to doubt citronella's utility is the 2009 study conducted by medical researchers at the Hebrew University in Jerusalem, Israel. Outdoors, citronella diffusers placed six metres from mosquito traps repelled female mosquitoes (which do the biting) by just 22 per cent. In contrast, the fragrant liquid alcohol linalool repelled females by 58 per cent. Even more impressive, the geranium oil extract geraniol repelled females by 75 per cent. "We concluded that geraniol had significantly more repellent activity than citronella or linalool in both indoor and outdoor settings," the authors said. The case for geraniol is further strengthened by University of Florida research conducted in 1999, which found that geraniol repels mosquitoes and other bugs of all stripes, from house flies to cockroaches. "After relying on Deet-based products for more than 40 years, this is a breakthrough that should revolutionise the market," says University of Florida insect expert Jerry Butler. Geraniol's high regard among experts may come as no surprise to gardening enthusiasts. After all, for centuries, canny gardeners have planted the pungent pink flowers in window boxes to ward off bugs. Other natural oil options include lavender, clove, cedarwood, tea tree and cinnamon leaf, which one study ranked better than the benchmark deterrent Deet. Essentially, it seems, the extract of any plant with a pong can potentially deter pests. Ditto picaridin is a synthetic chemical created by Bayer in the 1990s and recommended by the World Health Organisation. Like picaridin, oil of lemon eucalyptus scored top marks in a May 2015 survey conducted by the US buying advice service Consumer Reports. "Look first for products with 20 per cent picaridin or 30 per cent oil of lemon eucalyptus," the report said. "We think they're safer than those with Deet." Another reason to seek lemon eucalyptus is its pedigree. The refined version has long been deployed in China in a product called Quwenling. Deet, the dubious chemical concocted by the American military in the '40s, actually has its virtues, according to the London School of Hygiene and Tropical Medicine. University of California-Davis research shows Deet acts as a real repellent - mosquitoes intensely dislike its odour, which "jams" their sense of smell. If only Deet had more charm. The yellowy oil has some alarming traits, not least its ability to eat through plastic. Whether you decide to use Deet or a natural alternative, do use something because the humble mosquito, according to the World Health Organisation, racks up more than one million human kills every year, making it the most dangerous animal on earth.