Autocatalysis occurs when one of the products of a reaction acts as a catalyst for that reaction to occur more rapidly (or at a lower energy if you like). This results in an "acceleration" of the reaction.

An example of autocatalysis is the reaction of permanganate ion with oxalic acid to form carbon dioxide and manganous ion. Once this reaction has occurred the manganous ion acts as a catalyst to the original reaction. Such reactions are potentially dangerous, since the reaction rate may increase to the point of explosion.

The term autocatalysis is sometimes used outside of the context of chemistry to describe any effect which has results that make the original effect more likely to occur again.