Scratching an itch is far more common than itching a scratch. Both are grammatically correct, but the latter is considered informal. This is part of a complete episode.
gated adj.— «The new study suggests that itch, like pain, may be a “gated” system in which signals from other nerve cells can interfere with or moderate the sensation. Scratching the skin near, but not directly on, the spot that itches...
white n.— «If you itch in your genital area and also have a funny discharge from your vagina, you may have had candidiasis or what is commonly called “white.”» —“All You Need To know About ‘White'” Graphic...