The beta S globin chain binds at the valine site with complementary hydrophobic effects on other beta globin chain. This triggers the formation of polymers of haemoglobin. The rate of polymerization is increased with increase in intracellular deoxy-haemoglobin. Factors that promote polymerisation are dehydration, acidosis, increase in the level of 2,3 diphosphoglycerate which may occur in infections. On the other hand, the association of haemoglobin 5 with other haemoglobin that have higher oxygen affinity-like haemoglobin F or haemoglobin A reduce the rate of polymerisation.