As it happens with the case of lactose intolerance, this can cause uncomfortable reactions after drinking alcohol. Alcohol intolerance is caused by a genetic condition in which the body cannot break down alcohol efficiently. The only way to prevent this is to not to consume alcohol. This type of intolerance is not a true allergy as such; it might also be the reaction to something in an alcoholic beverage. It can as well appear if alcohol is combined with certain medications. Symptoms can include: flushing, hives, worsening of asthma, runny or stuffy nose, low blood pressure, nausea, vomiting and diarrhoea.