Significance:
Humidity refers to the amount of water vapour in the air. Moisture can physically and chemically affect medicines, especially solids like tablets and powders. If a drug or one of its excipients is hygroscopic (absorbs water easily), moisture uptake can cause clumping, swelling, coating breakdown, or physical disintegration. Chemically, the absorbed water can speed up hydrolysis reactions, where water molecules split chemical bonds in the active ingredient, reducing its potency. This is why medicines stored in bathrooms or kitchens often degrade faster than those stored in cool, dry places.