Darkened regions of the skin occur as a result of abnormal tanning when the skin is sensitive to sunlight. Several diseases and many drugs can occasionally cause photosensitivity. Among the common drugs responsible for photosensitivity are birth control pills, antibiotics (sulfonamides and tetracyclines), diuretics, nonsteroidal anti-inflammatory drugs (NSAID), pain relievers, and some psychiatric medications.
Darkened spots on the skin come in several varieties. The most ominous is malignant melanoma, a very aggressive cancer that can begin as an innocent mole. The majority of moles (nevi) and dark spots, however, are benign (harmless). The average person has several dozen, and certain people with a hereditary mole condition may have hundreds.
Any dark spot that is either new or changing should be evaluated by a dermatologist.
None of the above is intended as medical advice. If you have a medical concern, please consult your doctor.