Relative humidity, usually abbreviated RH, is the amount of water vapour present in the air expressed as a percentage of the maximum the air could hold at that temperature. It strongly affects food storage and processing: high humidity encourages mould growth on grains, dried foods, and cheeses, while low humidity dries out fresh produce, meats, and baked goods, causing weight loss and staling. Warehouses, cold stores, drying rooms, and ripening chambers therefore control RH precisely, balancing moisture loss, microbial risk, and product quality, and packaging specifications often assume a defined humidity range.