Why do bananas turn brown over time?

Bananas turn brown due to a natural process called enzymatic browning. When the peel or flesh is damaged or exposed to air, enzymes like polyphenol oxidase react with oxygen to produce melanin, which causes the brown colour. Additionally, as bananas ripen, the starch in the fruit converts to sugar, softening the tissue and making it more prone to bruising. This process is accelerated by ethylene gas, a hormone that bananas naturally release. While browning may affect the appearance, it often makes the banana sweeter and ideal for baking or smoothies.