Glad you are getting relief from using Benadryl. As you explore the possibility that this is an allergy, it may be helpful to examine the ingredients in your shampoo and experiment using shampoos that don't have certain ingredients. I found that I was allergic to a common ingredient called Sodium Laurel Sulfate (SLS). Using shampoos that don't have this ingredient has helped tremendously. SLS is not the only chemical in shampoos that people react to, there are others. SLS is just the one that triggers me. I hope this helps. P.S. This chemical is also commonly used in toothpaste and can cause problems in the mouth for some individuals.I wish you the best as you work to determine what is happening.