Vata, Pitta, K
apha are the three doshas. They destroy and support (sustain, maintain) the body when they are abnormal and normal respectively.
Reference: Ashtang Hriday
The doshas are material substances present in the body always, they have their own definite pramana (quantity), guna (quality) and Karma (functions). When they are normal (avikrit) they attend to different functions of the body and so maintain it. They have tendency to become abnormal (vikrit) undergoing increase (vruddhi) or decrease (kshay) in their quantity, one or more of their qualities and functions. When they become abnormal they vitiate their places of dwelling-the dhatus (tissues); because of this tendency of vitiation, they are called doshas or vitiators.