A quack is someone who offers medical treatment or advice without the qualifications to do so. As a general rule, quack is a derogatory term, and an accusation of quackery can result in serious punishments, as the unlicensed practice of medicine is punished very severely in most countries. The term “quack” is also used more generally to refer to someone who lacks scientific qualifications but speaks about scientific issues anyway.
The word “quack” is a shortening of “quacksalver,” a Middle English word which was used to describe people who sold various nostrums and other products at fairs and markets. Typically, quacksalvers announced their wares in penetrating, loud voices, making a variety of exuberant claims to attract customers, so one can see how the word evolved to refer to an unlicensed practitioner of medicine. “Quacksalver,” incidentally, comes from a Dutch word which means “boasting.”
Quackery is probably as old as the practice of medicine itself, although it rose to new levels in the 18th and 19th centuries, when an explosion of patent medicines plagued many countries in Europe and the United States. Many people saw the potential for turning a quick profit, and turned to sales of patent medicines and the dispensation of medical advice as a way to make a living. In the late 19th century, some attempt at regulation started to emerge, and today quackery is treated as a crime, typically prosecuted as health fraud.
Some very notable physicians were accused of being quacks in their day; Louis Pasteur, for example, was laughed at and called a quack for proposing that food could be sterilized with the application of heat, although pasteurization is an accepted and widely used practice today. In these instances, accusations of quackery were the result of radical ideas or an improper understanding of a concept.
There is some dispute about the boundaries of quackery. Some practitioners of allopathic medicine, for example, consider alternative and complementary medical practitioners to be quacks, railing against treatments ranging from acupuncture to the use of magnets in medical therapy. Many of these accusations stem from legitimate concerns about the efficacy of treatments, based on poor performance in empirical testing.
Due to concerns about quackery, all forms of health care are carefully monitored for advertising and claims which could be considered misleading, and only someone with a medical degree can dispense medical advice, prescriptions, and information. For this reason, many people who practice alternative medicine are severely limited; a massage therapist can work on strained muscles, for example, but he or she cannot legally offer medical advice such as nutritional recommendations to the client.