The irregularity in the shapes of the red blood cells causes them to get clustered together and being unable to move. This in turn results in the sickle cells getting stuck in the blood vessels (usually small vessels) like arteries and capillaries which can block or hinder the supply of normal oxygen-carrying blood to some parts of the body. Since the sickle-shaped cells are not flexible and cannot change their shape easily, many of them burst apart while moving through the blood vessels. The sickle cells can last from 10-20 days while the normal blood cells last for 90-120 days. This causes a rapid loss in red blood cells (as the sickle cells are still red blood cells, deformed as they may be) which the body may not be able to recuperate as swiftly from. This condition of sickle cells dying in smaller duration than required is what causes the phenomenon called anaemia.