In the current scenario of leprosy elimination, lepra reactions (LRs) remain a major persistent problem. Type 1 LR (T1LR) and type 2 LR (T2LR) are the major causes of nerve damage and permanent disabilities. The immunopathogenesis of LR have recently become an important field of research, since it may provide the relevant targets for the early detection and control of these episodes. Presently, there are no uniformly acceptable laboratory markers for LR. Genetic and serum markers in human host may predict susceptibility to reactions as well as progression of nerve damage in leprosy. Therefore, a deeper understanding of the molecular mechanisms involved in LR may provide a rational strategy for early diagnosis and prevention of the catastrophic consequences of LR.