Known as an insect repellent, Scientists were not sure how it worked until now. DEET does not so much repel mosquitoes and ticks which are attracted to carbon dioxide, and other human odors which give a signal that there is a blood supply somewhere, It masks these signals so the mosquitoes go and look for their blood supply somewhere else.
DEET has been available to the to the public,for over 50 years and is an active ingredient in many insect repellents, but adverse health effects have been noted such as rashes and seizures, is toxic to some marine species. The risk of DEET side effects are generally rare and must be matched with the risk of mosquito borne disease. Advice is given to avoid using on broken skin, and to wash off if no longer needed.
The standard warning on an insect repellent can. I've always found that any itch or sting from an insect repellent is better than the itch of a mosquito bite.