(Agraco) Now protect yourself with this all-natural repellent patch, the same patch used by U. S. Marines and the Australian Army. Each patch contains 300 mg of Vitamin B1. Research has shown that mosquitos, gnats, and flies do not like the smell of vitamin B1 excreted through the sweat glands. Goes to work in as little as 2 hours and lasts for over 36 hours. Contains no chemicals, pesticides, or insecticides.