Rash on my Dogs ear

Our dog has been scratching his ear. We have just been bathing it and it seemed to settled but today it has just flared up. We have done all the allergy testing through vets etc but nothing is coming back. We have also been giving him piriton

Hello - At risk of being a pedant (scientist - sorry!) I am intruiged by the term 'all the allergy testing etc' and wonder what specifically you are referring to, and what was found.  Perhaps a biopsy or IgE test indicated that an allergy was / was not likely, for example? - if so, what else was tested and what showed up?  I am also a pedant about the term 'nothing,' because while tests can exclude things or make certain outcomes less likely, 'nothing' is rarely a test result.  One might, however, find for example 'that a skin scrape was negative for sarcoptes.'  Did your vet run specific tests to check your pets' response to specific allergens?  It may help to ask specifically what has been done so far and what this rules in or out, and with what degree of certainty.  Most itchy ears are linked to allergy, but 'allergy' is difficult and complicated to test for.  Other causes include fleas, mites, foreign bodies down the ear and pain in all sorts of places, including dental pain.  A good question for your vets may be:  can you make a list of all the possible causes of my dogs' ear changes?  What have you ruled out so far?  What can't you rule out yet?  What further treatments or investigations would you recommend at this time?  Hopefully, this will help to set the investigation or treatment in some direction for you.