What could allergic reaction to alcohol be?

Hi, what could allergic reaction to alcohol be? If a person is experiencing rash all over the body when drinking alcohol, is it sign of allergic reaction?

Hi, there are some people who are allergic to alcohol. My ex-husband has been drinker for many years, but one day he got anaphylactic reaction to alcohol. He had gone ashen, he had very difficult breathing and was convulsing. His life was in great danger, and he barely survived. His condition was followed for a while, and he got some medications. He got Enephrine prescribed, to keep it with him all the time. He still drinks but not that much, although I hoped that he could quit it finally.