Some gnats do bite. The kind that are called "biting midges" and "no-see-ums" can cause a painful bite that takes longer than a mosquito bite to heal. Because they're tiny, gnats can be a more tricky opponent than other biting bugs.
You can reduce the amount of gnat bites you receive by limiting the time you spend outdoors when gnats are most active. Avoid the gnats' favourite times of day: dusk and dawn. In hot climates, where biting gnats are a problem, plan to be back from your evening walk before the sun begins to set, and postpone early-morning gardening until the sun is well up.
Avoid the gnat neighbourhoods. Gnats need water to breed, so they're more common near lakes, rivers, and other bodies of water. Chose a spot for outdoor activities that is away from bodies of water so you do not get gnat bites.
Seal off your house. If biting gnats are getting into your living space, keep windows closed or replace regular window screening -- which gnats can fly right through -- with special, fine mesh screening available at home supply stores.
Turn up the breeze. Gnats cannot land and bite if it's even slightly breezy, so use fans to keep the air moving while you're on your porch or patio.
Gnat-proof your skin. Most gnats cannot bite through fabric, so keep your arms and legs covered, if possible. Gnats love to go for the face, neck, hands, wrists and ankles, however; use insect repellent containing DEET on those areas if you'll be outdoors during gnat biting hours. Petroleum jelly, especially the mentholated kind, can create an effective barrier that keeps gnats from landing and biting your skin.
Gnat species vary in different parts of the country; not every prevention method works on every type of gnat, so be willing to experiment. Treat gnat bites by washing the area with disinfectant soap, then applying calamine lotion and/or an antihistamine lotion. Lotions sold for the treatment of poison ivy often contain both calamine and antihistamine. After the first day, also treat the bites with an antiseptic ointment such as Neosporin, because gnat bites tend to become infected. Don't scratch!
Don't use DEET if you are sensitive to this chemical; try petroleum jelly as a barrier protection method instead.