DEET has been used as an insect repellent in the U.S. for more than 50 years. The Repel 100 uses a 98.1-percent deet formula to provide protection from mosquitoes, ticks, gnats, chiggers, no-see-ums and biting flies. Use in areas of high infestation or prolonged periods of outdoor activity for up to 10-hour of protection.