Few years ago we had a big problem with fruit flies. I was searching everywhere what was the cause. At the end I found out we were using organic soil for our flower pots. We immediately replaced the organic soil for regular and the problem was solved. No more fruit flies in our house. They are really annoying and you possibly can get health issues from them such as diarrhea or stomach pains, because the lay their eggs to all this food they find inside your house and than you end up eating it.