How do you explain this man's persistently dry lips?

Case 2:
For several months, this 64-year-old man has had persistently dry lips despite frequent application of lip balm. He is otherwise healthy, and the lips are asymptomatic except for the dryness. Examination reveals that the dryness is confined to the lower lip.

This patient had actinic cheilitis, B, confined to the lower lip, which is the characteristic site of sun damage to the lips. He was given 5-fluorouracil to apply only 3 times a week to reverse the precancerous changes.

Lichen planus usually presents with a whitish plaque on the lip that does not wipe off (unlike the white plaque associated with candidiasis), and typically the buccal mucosa is involved as well. Contact dermatitis usually affects both the upper and the lower lip. Angioedema would be associated with edema, which was not present in this patient.