As long as the background isn't spilling light on your subject (unless that's the look you are trying to produce, it is fine).  Are you trying to isolate? If so, create a curves layer in PS and slide the left graph handle all the way to the right.  The area you want white should still be white.  If it's not clean it with the dodge tool or paint it white.  Along any edges use your the edge of a feathered dodge tool to make sure you have clean edges around your subject.  That will give you a true isolation.

Thank you this helps. I use the curves adj layer and than the white eye dropper- it really makes it white.

Quote from: tab62 on February 18, 2011, 14:11

Thank you this helps. I use the curves adj layer and than the white eye dropper- it really makes it white.

Doing it that way you'll run the risk of burning out the subject, better to overexpose the background 'in camera'. There are dozens of ways to get a white background and each person has their own preference, do what works best for you.

Agree, Using either levels or curves eye droppers results in the entire image being affected and lightened which most often is not the desired result.
Much better to get it as suggested 2 stops more light than the subject and thereby overexposing the background which should be at 255, 255, 255, anything else is not white.
Best tool to use for any cleanup is the Dodge tool set on Highlights and at 15-20%.
Best way to check background to ensure it is a true isolation, is to temporarily make a new adjustment layer, select levels, move the left (Black End) marker all the way to the right. Should end up with a hi-con looking like this, and if any cleanup is needed as is the case in this image use the Dodge tool to fix it, ensuring you have the background layer selected.
Then delete the adjustment layer