Bromelain is not a single substance, but rather a collection of enzymes and other compounds. It is a mixture of sulfur-containing protein-digesting enzymes, called proteolytic enzymes or proteases. It also contains several other substances in smaller quantities, including perioxidase, acid phosphatase, protease inhibitors, and calcium. It is primarily produced in Japan, Hawaii, and Taiwan, and most research has been conducted in the first two regions. However, Germany has recently taken a great interest in bromelain research, where bromelain is currently the 13th most widely used herbal medicine.

Bromelain is found most commonly in the stem of the pineapple plant (Ananas comosus). Pineapples have had a long tradition as a medicinal plant among the natives of South and Central America. However, just eating pineapple will not give you a great deal of extra bromelain, because it is mostly concentrated in the stem, which is not nearly as tasty (albeit still edible).

Bromelain can be used in a vast array of medical conditions. It was first introduced in this area in 1957, and works by blocking some proinflammatory metabolites that accelerate and worsen the inflammatory process. It is an anti-inflammatory agent, and so can be used for sports injury, trauma, arthritis, and other kinds of swelling. Its main uses are athletic injuries, digestive problems, phlebitis, sinusitis, and aiding healing after surgery. It has also been proposed in the use of arthritis, chronic venous insufficiency, easy bruising, gout, hemorrhoids, menstrual pain, autoimmune disorders, and ulcerative colitis. Studies have shown that bromelain can also be useful in the reduction of platelet clumping and blood clots in the bloodstream, especially in the arteries. It may even be useful in the treatment of AIDS to stop the spread of HIV. It has no major side effects, except for possible allergic reactions.

Other plant proteases include papain (from the papaya), actinidin (from the kiwi fruit), and ficin (from figs). These proteases may induce a prickly sensation in the mouth when consumed.