It was an interesting article posted on the New York Times news service: "People whose faces turn red when they drink alcohol may be facing more than embarrassment. The flushing may indicate an increased risk for a deadly throat cancer, researchers report."
There are other indicators, including nausea and a rapid heartbeat, which may or may not appear in such cases. The problem comes from an inherited deficiency in an enzyme called ALDH2, and can mostly be found in people of East Asian ancestry.
This deficiency results in an inability to metabolize alcohol, which leads to an accumulation in the body of a toxin called acetaldehyde.
Some people have such violent reactions that they are unable to consume large amounts of alcohol. The ironic part is that this reaction actually protects them against the increased risk of cancer since they can't consume too much and become heavy drinkers.