Hi.. Thanks for the query... Pemphigus vulgaris is an inflammatory disease causing sores and inflammation.. Due to inflammation only there is pain inside the mouth.. Do not worry as gradually when the sores will heal the inflammation will also subside and you will not feel pain.. As of now he can start gargling with mouthwash like Magic mouthwash as it will reduce inflammation as well as numb the inside of mouth that will reduce pain and also ease the burning during meals.. Start rinsing the mouth will cool water.. Avoid spicy, hot and irritant foods.. Consult your oral physician for an in person examination of there is no improvement in a week.. Hope this helps.. Regards..