My head hurts when i drink alcohol, why?

Blood vessel dilated: alcohol both directly and via a metabolite causes blood vessels to dilate, particularly in skin but also in the brain. The metabolite that does this, acetaldehyde, is poorly metabolized by some people, who tend to get both skin flushing and headaches, and even dizziness and fainting from low blood pressure. This is more common in Asians and Native Americans, but can occur in others. Stop drinking.