Idiosyncrasy

Idiosyncrasy, from Ancient Greek, idiosynkrasía, "a peculiar temperament", "habit of body" (, idios "one's own", , syn "with" and krasis "mixture") is defined as an individualizing quality or characteristic of a person or group, and is often used to express eccentricity or peculiarity. The term can also be applied to symbols. Idiosyncratic symbols mean one thing for a particular person, as a blade could mean war, but to someone else, it could symbolize a surgery. By the same principle, linguists state that words are not only arbitrary, but also largely idiosyncratic signs.

Disease
Idiosyncrasy defined the way physicians conceived diseases in the nineteenth century. They considered each disease as a unique condition, related to each patient. This understanding began to change in the 1870s, when discoveries made by researchers in Europe permitted the advent of a 'scientific medicine', a precursor to the Evidence-Based Medicine that is the standard of practice today.

Pharmacology
In contemporary medicine (as of 2007), the term idiosyncratic drug reaction denotes a non-immunological hypersensitivity to a substance, without connection to pharmacological toxicity. Idiosyncratic stresses here the fact that other individuals would react differently, or not at all, and that the reaction is an individual one based on a specific condition of the one who suffers it. Most commonly, this is caused by an enzymopathy, congenital or acquired, so that the triggering substance cannot be processed properly in the organism and causes symptoms by accumulating or blocking other substances to be processed. An idiosyncrasy causing symptoms like an allergy is also called pseudoanaphylaxis.

Psychiatry
In psychiatry, the term means a specific and unique mental condition of a patient, often accompanied by neologisms. In psychoanalysis and behaviorism, it is used for the personal way a given individual reacts, perceives and experiences a common situation: a certain dish made of meat may cause nostalgic memories in one person and disgust in another. These reactions are called idiosyncratic.