Homoeopathy considers pathology from a chronic disease perspective. Hahnemann developed the concepts of miasms and latency to explain chronic diseases. He associated psora with many chronic skin and internal diseases. Hahnemann was ahead of his time in recognizing infectious diseases as caused by microscopic organisms and parasites. He viewed disease as a dynamic disturbance caused by morbific agents internal or external to the body, and treatment as removing these agents' effects through antidotes that cause similar symptoms. Hahnemann's theories of the underlying causes and mechanisms of chronic diseases have been largely validated by modern science.