In outer space—no one can hear you sigh

From Quora:

Question:

How cold is outer space? Would someone die if they were to be bare-skinned in outer space?

Answered by Simon Gardner, minimalist, lateral thinker

The "reverse wind chill factor" (ie space is a vacuum), means there is nothing to convect your body temperature away which means even though it's very cold, this wouldn't kill you.

Your skin is enough the prevent the low pressure from making your bodily fluids boil.

Source:

nasa.gov

Human Body in a Vacuum

If you don't hold your breath, you're likely to survive uninjured for about 30 seconds. If you do hold your breath, you're like to suffer lung damage from the pressure differential.

One way or another lack of oxygen will be what gets you first.

If you do have breathing apparatus of some sort (that is designed so as not to over-pressurise your lungs) then you could probably last quite a while but it definitely wouldn't be good for your health. It might even be sunburn that kills you.