1. The periodic loss of the outer cuticle of arthropods and other members of the clade Ecdysozoa (e.g. nematodes, onychophorans, and tardigrades) to enable growth and metamorphosis within the constraints of a hard body covering. It starts with the release of enzymes from underlying cells that loosen the inner part of the old cuticle, followed by the formation of a new soft cuticle. The remains of the old cuticle then split; the animal emerges and absorbs water or swallows air and increases in size while the new cuticle is still soft. This cuticle is then hardened with chitin and lime salts. In insects and crustaceans ecdysis is controlled chiefly by three groups of hormones: ecdysteroids, such as ecdysone; neuropeptides, such as eclosion hormone and ecdysis-triggering hormone; and sesquiterpenoids, such as juvenile hormone.

2. The periodic shedding of the outer layer of the epidermis of reptiles (except crocodiles) to allow growth to occur.