People use insect repellents to reduce the chances of being bit by mosquitoes, particularly those that might be carrying an illness such as West Nile Virus or Malaria. People should apply insect repellent anytime they are outside, even if they do not see any mosquitoes around. When it comes to re-applying the repellent, the rule of thumb is to do so whenever you start getting bit. This will be more often if you sweat a lot or have been swimming.

Insect repellents work by making the odour of human skin undesirable to the female mosquitoes that are looking for the blood of a human in order to produce her eggs. While the repellent will keep the mosquitoes from biting, it does not kill them and they will still be flying around.