The more it itches, the more you scratch, the more anxious you get, the more tense, the more it itches. It is absolutely essential to break the anxiety reinforcement cycle, whatever the illness. The easiest way to do this is with breathing and biofeedback. Normally you inhale and exhale equally. In anxiety you take shorter, faster breaths.
Inhalation is longer than exhalation.
When you breathe, inhalation is a contraction state, the diaphragm and the chest muscles contract. Therefore you try to stay in the exhalation state longer than in the inhalation state. Breathe in at the count of 4 and out at the count of 6. As you exhale let that be a signal to relax the whole body. Raise your hand or finger, count 3 breaths, and at the count of 3 drop the finger and let that be a signal to relax the jaw and body.