Derm Dx: Pruritic hyperpigmentation of the lips

A 22-year-old woman presents with pruritic hyperpigmentation of her upper and lower lips that began approximately 2 weeks previously. She has no other systemic complaints, and vital signs are within normal range. The patient was prescribed oral doxycycline for treatment of recurrent acne 3 weeks previously and denies use of other medications or past adverse drug reaction.