Butylated hydroxytoluene (BHT) is a food additive which is used as a preservative, and when it appears on food labels, it indicates that the manufacturer is concerned about the potential for the food to go rancid. BHT is also used as a preservative in a number of other things, ranging from cosmetics to jet fuel. The substance was developed in the late 1940s, and approved for use in the 1950s.

This substance is an antioxidant, preventing oxidation damage to fats. When foods which are high in fat are not treated with preservatives, the fats can go rancid very quickly, causing the fats to taste bad, and potentially creating health risks for consumers. By using preservatives like BHT, manufacturers can ensure that their foods are shelf-stable longer, and that their flavors will be retained. Essentially, BHT intercepts free radicals, preventing them from attacking the fats.

BHT often appears in things like potato chips, which tend to be high in fat, along with baked goods and a wide variety of other foods. In cosmetics and other products, BHT works in the same way, protecting the fats in the product from damage which could cause the product to separate or go bad in other ways. In some instances, a related substance known as butylated hydrooxyanisole (BHA) may be used instead of BHT. BHA began displacing BHT in the 1970s, due to concerns about the health risks of BHT.

In pure form, BHT is a crystalline white power. It is highly fat soluble, allowing manufacturers to mix it into food as it is produced so that consumers will not notice the appearance or flavor of BHT. Like other food additives, BHT must be identified on a label; you may also see it identified as E321 in the European Union, which uses a system of numbers to mark various food additives.

The health risks of this food additive are a topic of debate, and further research is clearly needed. Some studies have linked BHT with an increase in tumors and malignant cancers, while others have suggested that it may help to protect the body from free radicals which cause other cancers. BHT also seems to have some antimicrobial and antiviral activities, and it has in fact been used in medical research for treating conditions like herpes. The Food and Drug Administration still considers BHT to be safe, although consumers who wish to avoid it may want to check their labels carefully.