Idiopathic itching is when your dog scratches but you are unable to find a reason for his/her discomfort.  Many vets will recommend giving Benadryl or even prednisone.  All these medications impair your pet's natural ability to remain healthy.  We work with our clients to help identify causes of the itching - but meanwhile - relief is needed.  Here is a nice and gentle recipe:
Chamomile tea brewed strongly (if there are sores or a rash we recommend adding slippery elm (about 1 part slippery elm to 3 parts chamomile).  Brew the tea by bringing water to steamy - NOT BOILING.  Then add the herbs or tea bags and let the tea steep.  We use loose chamomile flowers and shredded slippery elm bark.  We leave the herbs in the mixture and merely use a cotton ball dipped in the liquid to apply to skin.  Can be applied as often as needed.