Here is an article discussing how long a person could survive in space without a protective suit on.

The short answer is – not long: about 15 seconds.

There are several ways that you could die in these circumstances:

• If you try to hold your breath in the vacuum of space your lungs will rupture and you’ll get a mean case of the bends.
• If you don’t hold your breath (breathe out as much as you can), you’re not going to last too long either.
• Because of the very low pressure moisture would start to boil. For instance:
  

  “One NASA test subject who survived a 1965 accident in which he was exposed to near-vacuum conditions felt the saliva on his tongue begin to boil before he lost consciousness after 14 seconds.”

• There are also some pretty extreme temperatures in space: -130 C to 90 C. However, in a vacuum the body loses heat very slowly so this is unlikely to kill you too quickly.
• Finally, the article mentions a “spake hickey”:
  

  “Caused from the swelling and bursting of the skin’s small blood vessels”