Bananas help to ripen other fruit by releasing a special hormone called ethylene. Bananas are not the only fruit that has this effect. Apples, kiwis, tomatoes, figs and pears also produce ethylene. Fruits that produce ethylene are known as climacteric fruit.
Bananas are medium-level producers of ethylene, but they gained their reputation for ripening fruit because they are larger than many other climacteric fruits. Fruits placed near bananas respond to the ethylene emitted and begin to ripen as well. As bananas release ethylene, their respiration rates rise, and their pigment changes as they release sugar. After this point, bananas are more susceptible to decay and mold.