Differential Diagnosis for Black and Brown Skin under Armpit

Single Most Likely Diagnosis

• Hyperpigmentation (Post-Inflammatory or Melasma): This condition is characterized by patches of skin becoming darker than the surrounding areas, often due to inflammation or hormonal changes. The armpit area can be prone to friction and irritation, leading to post-inflammatory hyperpigmentation.

Other Likely Diagnoses

• Acanthosis Nigricans: A skin condition marked by dark, velvety skin patches, typically in the folds and creases of the body, which can include the armpits. It's often associated with insulin resistance and obesity.
• Erythrasma: A bacterial or fungal infection that causes brown or black patches in the folds of the skin, including the armpits, due to the warm, moist environment.
• Contact Dermatitis: An allergic reaction or irritation caused by deodorants, soaps, or other products used in the armpit area, leading to darkened skin.

Do Not Miss Diagnoses

• Malignancy (e.g., Melanoma or Other Skin Cancers): Although less common, any unusual skin changes, including new or changing pigmentation, should be evaluated for the possibility of skin cancer.
• Addison's Disease: A rare endocrine disorder where the adrenal glands do not produce enough cortisol and aldosterone, leading to hyperpigmentation among other symptoms.

Rare Diagnoses

• Argyria: A rare condition caused by exposure to silver or silver compounds, leading to a bluish-gray discoloration of the skin, which could potentially appear black or brown in certain lighting conditions.
• Hemochromatosis: A genetic disorder characterized by excessive iron accumulation in the body, which can lead to skin pigmentation changes, among other symptoms.