Unless broken down in the body system, alcohol is toxic to our body and an immediate immune response is triggered causing symptoms typical to an allergy.
An intolerance may arise when the body is lacking an enzyme that is needed to properly digest and eliminate a food or substance like alcohol. More commonly, symptoms caused by intolerance to alcohol , or to the food on which the drink is based (e.g. grapes for wine, grains for whisky etc.), or to another substance in the drink. If the alcohol molecule cannot be taken by the body system, it can cause unusual symptoms to occur.
Alcoholic beverages contain a complex mixture of grape, yeast, hop, barley or wheat-derived substances, natural food chemicals (like salicylate), wood-derived substances or preservatives like sodium meta- b-i sulfite. Fining agents might also be added to remove particulate matter.
These include the use of egg protein in some wines or seafood proteins to fine some beers. All these substances can be intolerant to the body.