Is there any history of trauma or injury to
You could be having an allergic reaction to
some substance to
which you are either constantly exposed or to which you are being exposed again and again.
What other symptoms are you having? Let us also know if you ahve any past history of any allergic reaction or any family history of allergies, etc.
This could also be due to lip biting, lip licking, sun exposure, vitamin or mineral deficiencies, dehydration, etc.