No doubt, you've had a bad hangover – with the headache, drowsiness, nausea, and dry mouth to show for it – and you can probably understand why there are numerous hangover "cures" on the market and countless home remedies promoted on the Internet. But here's a little secret: Most of the cure-alls don't work. While many of these are effectively snake oil, and others only mask the effects, science does gives us some answers to that pounding question: What, exactly, is a hangover, and, more importantly, how do we get over it?\r\nHangovers are caused by a combination of factors, most notably dehydration, says Dr. Gary Murray, program director for the Division of Metabolism and Health Effects at the National Institute on Alcohol Abuse and Alcoholism. As you may know from the excessive bathroom visits during a night of drinking, alcohol is a diuretic – a substance that promotes the production of urine. When everything is functioning normally, the pituitary gland secretes vasopressin, a hormone that reduces urine output by helping the kidneys reabsorb water in the body. Alcohol, however, suppresses this so-called anti-diuretic hormone, causing water to bypass the kidneys and instead flow into the bladder and eventually out of the body.\r\nFor some people, hangover symptoms may also result from toxic effects, Dr. Murray says. When you consume alcohol, enzymes break down the drink's ethanol into acetaldehyde; other enzymes then metabolize acetaldehyde into innocuous acetate. But some people, particularly those of Asian descent, have a difficult time breaking down acetaldehyde in that second step. The chemical compound builds to toxic levels, resulting in skin flushing, sweating, vomiting and rapid pulse. Some researchers suggest dehydration and acetaldehyde toxicity actually play very minor roles in producing hangovers. Instead, they argue that common hangover symptoms, including nausea, headache and fatigue, are the result of changes in immune function brought on by alcohol ingestion.\r\nOther factors that don't necessarily cause hangovers are thought to enhance the severity of them, such as sleep deprivation and smoking. Additionally, recent research has suggested that congeners in alcohol – byproducts of the fermentation process that contribute to the flavor, aroma and color of alcoholic drinks – may play some role in enhancing hangovers. For instance, one study showed that bourbon, which has a higher congener content than vodka, produces the more severe hangover.\r\nIn other words, the science is still out on the exact cause of hangovers and, given the many factors involved, there is likely no cure-all – each hangover may be unique to the individual's genetics, the drinks you imbibed and how well you've been taking care of yourself. But that's not to say that you can't diminish a hangover with a few simple tricks.