TBHQ is largely used in edible oils & fats & related food products. The underlying role of TBHQ is to retard the oxidative deterioration of these products, effectively extending their "shelf life".
TBHQ finds use in a variety of products such as essential oils, natural colours, confectionery, peanut butter, powdered dairy products, instant noodles, cosmetics, hair oils and many more.
TBHQ is particularly effective in stabilising unsaturated fats and oils, especially polyunsaturated frying oils. In frying oils TBHQ not only increases the number of fries possible per batch of oil, it also "carries through" to the fried food, effectively increasing the fried food's shelf life.
TBHQ is also used as polymerisation inhibitor for resins & unsaturated polyesters.