A friend was complaining about itch during meditation.
Here's a portion of our chat log.
Jagaro gives tips on his website on how to handle
this.
Itches
When sitting [in] meditation it's very common to get itches
somewhere on your body or face. Don't move to scratch it.
Instead sit with the itch and use it as a focus for your
meditation. It essence "scratch the itch with your
mind". Focus in on it, feel it, accept it and be
easy with it. Notice how it feels, notice your reactions to
it and the urge to want to scratch it. Watch the changing in
sensation and then watch it pass over time. Itches are a
wonderful way to be present with the changing conditions of the
body and how they manifest bodily sensations, feelings and emotions
in us, and how we have desire to do something about them or desire
to move away from them. This is where our practice is.
Next time you get an itch, even when you are not doing
sitting meditation, try this technique.
http://www.themindfulmoment.com/2010/09/meditation-technique-1-itches.html
He also had this to say:
There are two ways to deal with the itch. Continue to
focus on your normal breath meditation with the breath as the
meditation object and just leave the itch as something in the
background. The other way to deal with it is to put the
attention on the itch itself and make the itch the object of the
meditation. In this way the itch becomes the thing you are
focusing on. Dive into the sensation and feel it fully.
See all its detail and how the sensation changes.
So both of these are good ways to work with itches. Just
don't scratch it. ;-) In time the itch will just pass.
If it is an itch due to rash then the itch may continue
because there is a physical condition. You can however
eventually learn through meditation to experience the sensation as
just raw sensation and not as the irritation of emotion and mind
that we place on top of the itch (or pain).
Glad to have these tips from Jagaro 
And my own 2 cents : if it's discernibly a rash, then get
it treated too.
