How do you stop a Shihtzu who has a dustmite allergy from constantly licking its hind quarters?

This has been diagnosed by vet. Definitely not fleas! Dog put on half a steroid tablet per day by vet. Regularly hoovering bungalow. Trying spraying with lavender water at moment. Will try Tea Tree Oil. Dog has undergone a thorough health check by the vet.

It's great that you pinpointed the specific irritant and it would be impossible to completely remove dust mites from the dog's environment so you will need to provide supportive care. There are many antihistamines that you can use OTC. I have tried Benadryl, Claritin, Tavist and none have worked as well as Chlortrimetan. But it is a long process to figure out what works best for your dog and the vet will have to give you proper dosages. Steroids such a Prednisone are effective but also come with side effects and I did not want to keep my dog on it long term. And it is very important to follow the vets instructions regarding the steroids such as tapering off so you do not cause shock to the organ systems. You may also want to consult a vet dermatologist and as far as your home, thoroughly vacuum EVERY DAY and invest in a good household Air purifier.