Miasms as a cause of disease

Another important component of homeopathy is the concept of "miasms". Hahnemann hypothesized that certain illnesses leave behind some residual damage, or miasm (Greek for "stain" or "imbalance"), which is postulated to be responsible for chronic diseases, and is said to be passed on genetically. There are three types of miasms in homeopathy:

i.)"syphilis", resulting in damage to the brain, nerves, and bones, resulting in deafness, insanity, alcoholism, etc.
ii.)"sycosis", a term used in homeopathy to refer to suppressed gonorrhoea, damaging the mucous membranes and genital tract, producing sensitivity to damp weather and storms
iii.)"psora", damaging the skin, resulting in many types of internal disease states

Hahneman developed his miasm hypothesis because he was concerned about the failures of his homeopathic remedies to produce lasting cures for chronic diseases. By 1816, Hahnemann had noticed that "…the non-venereal chronic diseases, after being time and again removed homoeopathically … always returned in a more or less varied form and with new symptoms."

To explain this, Hahnemann introduced his miasmatic hypothesis. Hahnemann's miasm theory was first published in 1828 in his book, The Chronic Diseases, their Nature and Homoeopathic Treatment.

Hahnemann hypothesized that the miasm of psora underpinned most chronic diseases. The word "miasm" is related to an old medical concept known as the "miasma theory of disease", where the term "miasma" represents "pestiferous exhalations". Hahnemann described this in Note 2 to §11 of the Organon: "…a child with small-pox or measles communicates to a near, untouched healthy child in an invisible manner (dynamically) the small-pox or measles, … in the same way as the magnet communicated to the near needle the magnetic property."

According to Hahnemann, miasmatic infection causes local symptoms, usually in the skin. If these are suppressed by external medication, the hidden cause goes deeper, and manifests itself later as organ pathologies. In §80 of the Organon he asserted psora to be the cause of such diseases as epilepsy, kyphosis, cancer, jaundice, deafness, and cataract.

According to Hahnemann, the body can become susceptible to "morbific noxious agents" that cause disease. Homeopaths try to prevent disease, starting with the first symptoms, which can be displayed long before an acute disease appears. However, Hahnemann recognized that sometimes a large group of people are beset by the same acute disease simultaneously, perhaps because of wars, floods, and famines and other causes, and an epidemic ensues. Hahneman advocated administering one or even a few remedies to a population to prevent a threatened epidemic. According to Hahnemann, when an epidemic begins the homeopath can produce an appropriate remedy for each individual patient from a small collection of remedies.

However, the miasm theory was not widely accepted. Even in his own time, many followers of Hahnemann, including the American homeopathy pioneer Constantine Hering, made almost no reference to Hahnemann’s concept of chronic diseases and the miasm hypothesis. Today, some homeopathic practitioners find Hahnemann’s theory difficult to reconcile with current knowledge of immunology, genetics, microbiology and pathology, as it seems to ignore the importance of genetic, congenital, metabolic, nutritional, and degenerative factors in sickness. The miasm theory also fails to differentiate between the multitude of infectious diseases. However, most insist that the key elements of Hahnemann's miasm theory are valid. For instance, most of them believe that the fundamental cause of disease is internal and constitutional (i.e. the susceptibility to becoming ill), and that it is contrary to good health to suppress symptoms, especially skin eruptions and discharges. They also accept Hahnemann's concept of latent psora, the early signs of an organism’s imbalance, which indicate that treatment is needed to prevent the development of more advanced disease.