My Great Dane has a rash that seems to be moving through his system from his back to his chest, which he keeps licking. He also has an extremely swollen snout and i have no idea what it could be. Is there a remedy for this and is it serious?

Any  rash  that  travels  could  be something  serious  to look  into , He  could  canine  onset  Steven  Johnson Syndrome  But  never  heard  of  it  in dogs  But  sure  sounds  like  something that  needs  attended  to