Alcohol hangovers are a commonly experienced consequence of drinking and are frequently associated with worsened mood and cognitive functioning. The physiological changes that occur with an alcohol-induced hangover state are largely unknown. This review focuses on key physiological factors of an alcohol-induced hangover, more specifically, oxidative stress, hormonal fluctuations, dehydration and changes to the immune system. The role of sleep disturbances and headaches will also be briefly discussed. Increased understanding of the relationship between the physiological factors and symptoms of a hangover is needed to further elucidate the mechanisms of an alcohol-induced hangover and potentially identify a treatment. The direct effects of the physiological factors occurring during an alcoholinduced hangover state should be further assessed under laboratory settings.