We have a skin issue which means our skin barrier has been manipulated and broken down. Thats why we cant naturally have hydrated lips. Any form of lubrication/moisturisation will provide relief and improve severity. Licking the lips is not the solution in fact this will most likely irritate an already irritated condition. Think of it like this would someone with dermatitis on their feet or hands go and lick it or lubricate it with saliva?
We have chilitis which just means inflammation which really just means we have a form of dermatitis.