Alcohol intolerance can cause immediate, unpleasant reactions after you drink alcohol. The most common signs and symptoms of alcohol intolerance are stuffy nose and skin flushing. Alcohol intolerance is caused by a genetic condition in which the body is unable to break down alcohol efficiently. The only way to prevent alcohol intolerance reactions is to avoid alcohol. Alcohol intolerance isn't an allergy. However, in some cases, what seems to be alcohol intolerance may be your reaction to something in an alcoholic beverage — such as chemicals, grains or preservatives. Combining alcohol with certain medications also can cause reactions.
The commonest abnormal reaction to alcohol is seen in persons from an oriental background, who get flushing, increased heart rate, and symptoms of reduced blood pressure. This is sometimes referred to as 'oriental flushing syndrome'. Approximately 50% of Chinese, Japanese, and Koreans are deficient in ALDH, and this has been reported to be protective against the development of alcoholism.
Allergic reactions to alcohol itself are rare, but described in a few dozen published case reports. As little as 1 ml of pure alcohol (equivalent to 10ml of wine or a mouthful of beer) is enough to provoke severe rashes, difficulty breathing, stomach cramps or collapse, a condition known as anaphylaxis. Given that the body constantly produces small amounts of alcohol itself, the reason that such reactions occur is poorly understood.