Can you turn off the blood in US Left 4 Dead 1 or 2

Unfortunately, there is no way to turn off the blood in either Left 4 Dead 1 or 2. However, you may have noticed that in Left 4 Dead 2, the survivors can literally cut of the heads, arms, and legs of the zombies. If you or your parents are disturbed by that, go to the settings, select "Audio/Video" and scroll down to gore. On default it will be set at high, you have the option to set this at low.

Edit: Please note that what this person said ONLY applys to Left 4 Dead 2