Conditioned taste aversion, also known as sauce béarnaise syndrome, is a phenomenon in which an individual develops an aversion to a certain food taste following a negative experience, typically illness. This form of aversion is a type of classical conditioning in which the taste of the food (conditioned stimulus, CS) is associated with the experience of illness (unconditioned stimulus, UCS).

A notable characteristic of conditioned taste aversion is that it often requires only a single exposure to the food that caused the sickness. For example, if a person eats sushi and later becomes ill, just this one negative experience can lead to a long-lasting aversion to sushi. This is unlike most forms of classical conditioning, which usually require repeated pairings of the CS and UCS.

In addition, there is often a significant delay between the ingestion of the food and the onset of illness. This delay can span several hours, typically up to six or eight hours. For instance, if someone eats sushi at noon and starts feeling nauseous by the evening, they are likely to develop an aversion to sushi despite the delay. This delayed response is an adaptive mechanism that helps individuals avoid foods that might be harmful, thereby preventing future bouts of food poisoning or similar illnesses.

Conditioned taste aversions are highly specific and tend not to generalize widely. This means that the aversion is usually limited to the specific food that caused the illness. For example, a person who develops an aversion to sushi after getting sick from it might still be able to eat other types of fish, especially if they are cooked differently. This specificity ensures that the individual can still enjoy a variety of other foods without associating them with the unpleasant experience.

Conditioned taste aversion is a protective mechanism evolved through classical conditioning, requiring only one instance of food-related illness to develop. This aversion can form even with a significant delay between the food intake and the onset of symptoms and is typically limited to the specific food involved, minimizing the risk of generalizing the aversion to other potentially safe foods.