1.Due to nutritional deficiencies the protective epidermis might have peeled first and then licking and biting might have innoculated/cultured some pathogenic species on that spot by providing necessary conditions.
2.licking on healthy epidermis might not cause any damage ,but if epidermis is lacking and we licked ,there are 2 possibilities,a)damage by salivary enzymes b)some pathogenic species might be growing there.
rule out : if it was a damage by salivary enzyme it might have initiated an inflammatory response, which should have been resolved with steroid ointments.(so its not immune related or salivary enzymes related)
-coming to pathogenic species may be bacterial/fungal/viral.these organisms are again sub divided into many categories which need a specific Antibiotics for specific pathogens.A single Antibiotic might not work for all because we don't know which particular pathogen has settled there. similarly many sub species of candida and viral are evolving day by day. a single broad spectrum Antibiotic /anti fungal may not do the trick we should care fully try one by one.
conclusion :It should be caused only by two reasons 1)inflammatory:some in the forum who gets resolved by steroid ointments(protopic/tacrolimus) had immune activated peeling and for the rest
2)pathogens:there were many cases in this forum whose lips would become normal with Antibiotic or antifungal(calendula ointment,fusidic ointment) ointments temporary.Its a very good sign if it is pathogen related issue ,then it is 100% curable.Only the thing which might create us doubt is why the condition reappears after discontinuing ointments,then the answer would be for any conditions the doctors would fix the time of treatment after clinical trials and for eg gram positive bacteria so and so antibiotic and decides the dosage form say might be for 3 days or 6months for tuberculosis etc