Arthropod-borne diseases are a real public health problem. One of these,
Lyme disease, is a bacterial infection due to Borrelia spp., transmitted by a hard tick, Ixodes spp.. The infection is particularly prevalent in the Northern Hemisphere and primary prevention relies on the use of repellents for cloth impregnation (pyrethroids) or for skin application (DEET). Pyrethroids and DEET are the two most studied repellents. The concentration of the active principle is essential to get a real repellent efficiency. The most efficient are: DEET at 30-50%, picaridin or KBR3023 at 20%, citriodiol at 30-50%, and IR35/35 at 20-35%. These molecules may induce adverse-effects. Considered for some time as cosmetics, a new European regulation now defines these molecules as biocides.