What kills you first in space?

A little morbid. But something I've never really asked or thought about, but suppose one went into space without a suit, what would kill you first, the lack of air, extreme temps, something else? And how long would someone last before death? I assume it's not instant, but I'd think it happens fairly quickly. I mean, we can hold our breath underwater for several minutes. I would assume less than a minute in space.