Unani system of medicine is based on the doctrine of humoral theory. According to this concept, each individual has a unique humoral composition, consisting of a mixture of all four humours with an ascendance of one of them, which functions as the representative of all humours in the body, and is referred to as having a sanguine, phlegmatic, choloric, and melancholic temperament. Phlegm is regarded as the best after humour blood because, in the absence of blood, balgham transforms into blood and is replenishing the organs. Phlegm has a cold-moist disposition and might be normal or pathological. Normal phlegm tastes sweet. According to Galen, regular sweet phlegm does not have a particular reservoir. Because it is remarkably similar to blood and is required for every organ in the body, hence transported in the blood. When the demeanor and taste of phlegm alter, it becomes aberrant and causes a variety of ailments. The etiology, pathological alteration, appearances, and symptoms of aberrant phlegm have been reported by ancient Unani physicians. The study attempts to build a knowledge of abnormal phlegm and its accompanying diseases based on the description found in the Unani literature.