phaneromania

from The Century Dictionary.

• noun An uncontrollable habit of picking at loose bits of skin, warts, hangnails, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun An uncontrollable impulse to pick at a spot or growth on one's body; the habit of picking at scabs, biting one's nails, or picking pimples.
• noun The constant preoccupation with some external part of the body, as plucking the beard, pulling the lobe of the ear, etc.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an irresistible desire to pick at superficial body parts (as in obsessive nail-biting)