The Environmental Protection Agency warned consumers against using insect repellents containing a pesticide that has been shown in studies to cause adverse health effects in animals. The pesticide, known as Insect Repellent-11, or R-11, and listed among active ingredients as 2,3,4,5-Bis, is commonly found in human and animal products to repel deer ticks, mosquitoes and other biting insects. The chemical is particularly effective against flies. An EPA spokesman said the pesticide is found in 25% of the repellents used in the United States. The two most common brand names that contain R-11 in some of their repellents are Off and Cutter. The manufacturers of those two brands are voluntarily recalling products that contain R-11, the EPA said. The active ingredient is used by 67 companies in about 200 products, but the agency said that most repellent products do not contain the compound.