The term “Miasm” or “Miasma” was used by the founder of Homeopathy, Dr. Samuel Hahnemann, for minute or microscopic, parasitical, living organisms, which we today understand as the microorganisms (bacteria, viruses, etc). The Miasmatic theory of Hahnemann considers the minute, parasitical, pathogenic living creatures (microorganisms) as the cause of acute infectious diseases (such as smallpox, measles, scarlet fever, cholera, anthrax, etc) and those chronic diseases that are not due to allopathic means of treatment, not associated with a person’s occupation, etc.
According to the Miasmatic theory of chronic diseases, developed and propounded by Dr. Samuel Hahnemann, there exists three chronic miasms or chronic miasmata or chronic miasmatic diseases, namely, – Psora, Syphilis, and Sycosis, all of which are caused by infectious microorganisms and transmitted through infection or inheritance (parents loaded with chronic miasm or miasms can transmit the miasmatic disease or diseases to the offspring in the form of genes).
Psora, Sycosis, and Syphilis present themselves initially as skin symptoms. When the skin symptoms are removed by local means or disappear themselves, the inner aspect of the chronic miasmatic disease still exists and never gets removed by itself or by any means except the use of proper anti-miasmatic homeopathic remedies. From time to time, the untreated, hidden, and latent internal miasmatic disease flares up producing varied and repetitive acute symptoms and a multitude of chronic diseases.
Thus, a person loaded with one chronic miasm or more chronic miasms, becomes predisposed to other acute and chronic diseases. This is the reason that a chronic miasm is also considered as a diathesis, dyscrasia, constituition of the patient, or predisposition to become chronically ill. The main value of the Miasmatic theory of Homeopathic system of medicine lies in the treatment of the chronic diseases of the human race.
Also, see the most complete definition of “nosode” at “What is a Nosode?”