The usual explanation of the term is, an oversensitiveness to one thing or a few things. There may be a chronic idiosyncrasy from a chronic miasm and an acute idiosyncrasy from an acute miasm. There are acquired idiosyncrasies and idiosyncrasies that are born with a patient. …

The study of the idiosyncrasies is closely related to Homoeopathy. The usual explanation of the term is, an oversensitiveness to one thing or a few things. It does not apply to the general susceptibility in feeble constitutions where patients are susceptible to all things, over-susceptible and over-impressed by simple annoyances. In the old school idiosyncrasies relate to certain patients who are known in every practitioner’s practice as oversensitive.

One oversensitive cannot take Opium for his pains, because of the congestion it produces, because of dangerous symptoms; he is oversensitive to it and has complication from a very small dose even and the physician is compelled not to administer it. Another patient cannot tolerate Quinine in chills and fever; the primary action of Quinine makes him alarmingly sick; where another individual may take 15 grains. One who has an idiosyncrasy to Quinine cannot take –a state of quininism.

The homoeopath recognizes of wide range in susceptibility, including things that the allopath is not acquainted with. There may be a chronic idiosyncrasy from a chronic miasm and an acute idiosyncrasy from an acute miasm. There are certain individuals in every community that cannot ride in the country because of their susceptibility to hay fever; others cannot bear the smell of flowers in the room because of becoming sick; some will get sick from the smell of roses.

I have known a number of patients who became sick in this way. It is common enough, and the sickness is known by the name of rose cold or rose fever. I have a patient who cannot have dry lavender flowers in the house without coming down with coryza. She is disturbed by two or three things in this way, and will go looking about to see which one of those things is in the house. I had another patient who could not have peaches in the room without becoming sick; one of the symptoms that he had was diarrhoea.

This oversensibility is very important and it explains in a measure the susceptibility to the remedy that will cure. If an idiosyncrasy to the remedy is not present, the patient will not be susceptible enough to be cured. The state in which he becomes sensitive enough to a drug to cure him is very analogous to these idiosyncrasies above mentioned. Think what susceptibility man must have to the remedy that cures him, when it cures in the very high attenuations that we use.

There are acquired idiosyncrasies and idiosyncrasies that are born with a patient. Those that are congenital and those that come from poisons are most difficult. In Rhus tox. poisoning those that have once been affected by handling it are so sensitive to it that if they go within a quarter of a mile of the vine, though they cannot detect it with the nose, yet in a few days they will come down with a case of Rhus poisoning. A very high potency of Rhus will sometimes remove that susceptibility and a dose of Rhus c.m. or m.m. will often check the acute poisoning from Rhus: but if you find that the patient has been born with a sensitivity to Rhus, while Rhus may palliate a few times it will finally cease to help him.

When one is born with this sensitivity it is very tenacious and will sometimes persist, in spite of our best endeavours, to the end of life. If eradicated at all, it requires an antipsoric to get to the bottom of it. Hay fever is brought on in the fall and is supposed to be caused by the patient’s over-sensitiveness to irritants that develop about that time; sometimes it is attributed to the hay that is curing in the fields at that time, sometimes to the different weeds that grow up then.

Such patients have often been able to ferret out the thing that they are susceptible to. But psora is at the bottom of all these troubles. Patients getting up from typhoid fever have often idiosyncrasies, and the chronic miasms are responsible for these, just as psora is prior to the sore eyes from scarlet fever. Sequelae are miasmatic, they are simply the outcroppings of chronic miasms.

There are persons who are sensitive, not merely to one or a few things, but to all things; oversensitive to the high potencies, oversensitive in taste, oversensitive to light, and a great many other things. This is a constitutional state; the patient is born with it. There are persons in whom you will see the sensitiveness only when you go away from the plane of nutrition into the plane of dynamics.

You will see for instance patients who will sit at the table and crave common salt; want lots of salt upon their food, and never seem able to get just exactly what they need. They eat plenty of common salt and remain sick, growing thinner all the time. This is on the nutritive plane; the crude common salt is taken with the food. Now you administer the c.m. to such a patient, and it makes that patient sick, producing a violent aggravation. This is where a food sustains a curative relation upon a higher plane. We step out of the nutritive plane into the plane of dynamics, the plane of disease- causes and cure.

James Tyler Kent
James Tyler Kent (1849–1916) was an American physician. Prior to his involvement with homeopathy, Kent had practiced conventional medicine in St. Louis, Missouri. He discovered and "converted" to homeopathy as a result of his wife's recovery from a serious ailment using homeopathic methods.
In 1881, Kent accepted a position as professor of anatomy at the Homeopathic College of Missouri, an institution with which he remained affiliated until 1888. In 1890, Kent moved to Pennsylvania to take a position as Dean of Professors at the Post-Graduate Homeopathic Medical School of Philadelphia. In 1897 Kent published his magnum opus, Repertory of the Homœopathic Materia Medica. Kent moved to Chicago in 1903, where he taught at Hahnemann Medical College.