This largely depends on how they are used. DEET, which is diethyltoluamide in full, can be harmful to the skin. While this is true, it’s also the most effective ingredient in repellents. Don’t use these products more than once in a day. It is also advisable only to use them as a second option after a repellent with another ingredient. All in all, it deals very well with mosquitoes, so you should put your state of health first and the risks it brings a second.