These are carvacrol and thymol. It has been shown that both of these have significant effects on harmful microorganisms that cause many illnesses. 

Please do not confuse Oil of Oregano with common oregano that is used as a herb for cooking. Common oregano is typically Origanum Marjoram, while Oil of Oregano is made from from Origanum Vulgare.

Oil of Oregano can be bought as either a liquid or as capsules. In both forms, it is important to check that the oil is from the proper oregano plant, and that it has a carvacrol concentration of at least 70%.

See Jini Patells Wild Oregano Oil Aniti-Viral Protocol for lots more information on how to use this wonderherb to cure flu bugs quickly, or prevent contracting them in the first place.

Jini has also put up the following report on the using wild oregano oil for Crohn's and Colitis.