Are you sure it is gnats? Do you see them or are you just being bitten? The reason I ask is that back in the UK I had a problem with being bitten and assumed it was gnats coming into the house. About a week later we realised, not gnats - cat fleas! Eeeeew! We did not even own a cat! The little rotters had laid eggs in the carpets and when they hatched, the cat fleas bit our ankles and legs. Apparently the previous house owner had cats and the flea eggs must have sat dormant in the carpet waiting for hot weather to hatch. We had to get the carpets sprayed professionally to get rid of the infestation!
I see them in the windows in the kitchen and no one has been bitten.
There are fungus gnats, small black and annoying. They come out of the soil of plants that are to wet, they only last a few days but lay hundreds of eggs that keep hatching. Then there's fruit flies, a little bigger and more brown - usually from ripe bananas or other fruit. For fungus gnats there are many products at most stores to take care of that problem. As for the fruit flies, get rid of the source. Also: http://www.ehow.com/way_5575453_fruit-fly-infestation-home-remedy.html
Set out a few little dishes of apple cider vinegar to which you have added a drop or two of liquid dish detergent. The fungus gnats are attracted to the smell, settle on the surface to taste, and the dish detergent makes it so they can't get out. They drown. Theresa is correct that they live in the soil of house plants. It can help if you let the top inch or so of soil dry out before watering.