What should you know about malignant acanthosis nigricans?

Acanthosis nigricans causes thickened, velvety, brown or darker skin, often in the neck, armpits, groin, or other folds. Common forms can be associated with insulin resistance, weight-related factors, medicines, or inherited tendencies. The malignant form is uncommon and may appear abruptly, spread widely, involve unusual sites such as the mouth or palms, or become more pronounced than expected. It can occur before, alongside, or after detection of an internal cancer, so the skin finding should not be dismissed as a cosmetic problem. [Dark Patches On Skin](/symptoms/dark-patches-on-skin/) describes the visible symptom, not its cause.

Arrange prompt review with a dermatologist or physician, particularly when the change is new, fast-moving, extensive, itchy, or involves the lips or mouth. The clinician may inspect the skin, review symptoms and medicines, ask about personal and family health, and coordinate further evaluation when indicated. Do not scrub aggressively or apply strong lightening products while the cause is unclear. Once the underlying issue is addressed, appearance-focused options such as [Topical Retinoids](/treatments/medical-dermatology/topical-retinoids/), [Chemical Peel](/treatments/aesthetic-procedures/chemical-peel/), or [Laser Toning](/treatments/laser-and-energy/laser-toning/) may be considered for selected people.

Seek prompt medical assessment for sudden darkening that spreads over weeks, involves several body areas, affects the mouth or palms, or appears with unexplained weight change, persistent abdominal symptoms, difficulty swallowing, or marked fatigue. Get urgent help for trouble breathing or swallowing, facial swelling, or rapidly worsening symptoms. These warning signs do not establish a diagnosis, but they make timely evaluation especially important.

Ask whether the appearance fits acanthosis nigricans, what common causes should be checked, whether the speed or distribution changes the evaluation, which symptoms to report, and when cosmetic treatment would be appropriate.