Research into the causes of Gulf War Illness looked at every possible chemical and/or drug that military personnel may have been exposed to during the conflict. There were literally hundreds of substances, and combinations thereof, examined. The 0.5 percent permethrin aerosol was available to personnel in-country during the 1991 war, but its use was minimal since most action occurred during the winter months when insect populations were low or nonexistent. To date, no substantive evidence exists to implicate permethrin as a cause of Gulf War Illness.