to the quick

to the quick

1. To the exposed flesh, especially that which is tender. I've bitten my fingernails to the quick, and still, I can't stop myself!
2. To the deepest, most fragile part of oneself. Typically used to describe emotional wounds. I can't even look at her right now—that hurtful remark cut me right to the quick.
See also: quick
Farlex Dictionary of Idioms.

cut to the quick

To be deeply wounded; to have one’s feelings hurt. The noun “quick” means the living, as well as the most vital and important part; today it also means the very sensitive flesh between the fingernails and skin. To be touched to the quick, meaning to be deeply affected, has been used since the sixteenth century; it appears in John Heywood’s Proverbs and in several places in Shakespeare’s plays (Hamlet, The Comedy of Errors, and others). Another version is stung to the quick, as in “The last appellation stung her to the quick” (Henry Fielding, Joseph Andrews, 1742). “Cut to the quick” is a still later wording and has been a cliché since about 1850. See also quick and the dead.
See also: cut, quick
The Dictionary of Clichés by Christine Ammer
See also:
  • flesh out
  • hang on by (one's) fingernails
  • cling on by (one's) fingernails
  • flesh
  • a nail-biter
  • biter
  • bitten by the same bug
  • flesh and blood
  • your flesh and blood
  • (one's) (own) flesh and blood
References in classic literature
My heart stood still at the thought, but mind and muscle responded to the quick decision I was forced to make.
* Redesigned medium wheel loader-based machine provides improved lines of sight to the quick coupler and work tools
Developed to help meet processors' increased interest in JIT (Just-In-Time) manufacturing, these systems are a natural complement to the quick tool-changing systems already developed for this need.