There are several medical conditions that can cause changes in skin pigmentation. Some of the most common conditions include: Vitiligo: This autoimmune condition causes the skin to lose pigmentation, resulting in white patches or depigmentation on the skin. Melasma: This condition causes brown or gray patches on the face, typically due to hormonal changes or sun exposure. Post-inflammatory hyperpigmentation: This occurs as a result of skin inflammation or injury, such as acne, eczema, or psoriasis. Albinism: This genetic condition affects the production of melanin, resulting in little or no pigment in the skin, hair, and eyes. Tinea versicolor: This fungal infection can cause patches of skin to become lighter or darker than the surrounding skin. Addison's disease: This hormonal disorder can cause a darkening of the skin, particularly in areas of the body that are exposed to the sun. Drug-induced pigmentation: Some medications, such as certain antibiotics, antipsychotics, or chemotherapy drugs, can cause changes in skin pigmentation.