Of these, DEET is the most effective, and best studied, synthetic insect repellent currently on the market. It has a remarkable safety profile after 40 years of worldwide use, although toxic reactions are known to occur. Developed by scientists at the U.S. Department of Agriculture and patented by the U.S. Army in 1946, it was subsequently registered for use by the general public in 1957. According to the estimates of the U.S. Environmental Protection Agency, more than 38% of the U.S. population uses a DEET-based broad-spectrum insect repellent every year and its worldwide use exceeds 200000000 people annually.DEET is available in 5% to 100% concentrations in multiple formulations, including solutions, lotions, creams, gels, aerosol and pump sprays, and impregnated towelettes. Products with 10% to 35% DEET will provide adequate protection under most conditions. Products with concentrations around 10% are effective for about two hours, concentration of 24% protects for about 5 hours and the efficacy plateaus at a concentration of about 30%. Generally DEET should be applied once a day and the lowest concentration effective for the amount of time spent outdoors should be chosen, especially for children. Use of 20% DEET is considered to be safe in pregnancy. In children, 30% DEET or less are considered to be safe, but these are not recommended for use in infants younger than 2 months.