Everyone knows you feel warmer once you’ve had a few drinks, but why? Is it just because being inebriated stops you from feeling cold?
Actually there’s more to it than that. Alcohol is a vasodilator, it makes our blood vessels widen when we drink. This means that more blood can flow through our arteries and veins and get to everywhere in our bodies, including to the skin and the extremities. Since our blood is a toasty 37 degrees Celsius (give or take) this will help make our skim feel warmer, even if it’s chilly outside. That’s the beer jacket effect. It’s also why people often look flushed or think they get a rash from drinking, and why long-time alcoholics have persistent red noses and cheeks (even when they’re not drunk – the blood vessels actually burst).
In actual fact though the beer jacket effect really make us colder! By allowing more blood to the surface we lose some of our body heat to our surroundings and our core temperature drops. (In the cold our blood vessels normally tighten to keep our blood away from the surface, which is why fingers and toes might go numb and look white in the winter.)
The opposite of vasodilation is vasoconstriction of which caffeine is a prime cause. Caffeine withdrawal headaches are caused by the blood vessels opening back up allowing blood to rush into your brain.