Which condition is characterized by dark patches of brown or black on the skin?

The condition characterized by dark patches of brown or black on the skin is malignant melanoma. This type of skin cancer arises from melanocytes, the cells that produce melanin, which gives skin its pigment. Malignant melanoma is particularly notable for its dark coloration, often appearing as a new mole or a change in an existing mole. The darkness is due to the excess melanin produced by the melanocytes when they become cancerous.

Identifying malignant melanoma early is critical, as it can be highly aggressive and spread to other parts of the body if not treated promptly. The primary visual characteristic to look out for is the presence of these dark patches, which can vary in size and shape but will often display irregular borders.

In contrast, other skin conditions listed, such as basal cell carcinoma and squamous cell carcinoma, typically present differently. Basal cell carcinoma usually appears as a pearly or waxy bump, while squamous cell carcinoma may show up as a firm, red nodule or a flat lesion with a scaly, crusty surface. Actinic keratosis, on the other hand, is characterized by rough, scaly patches that can be a precancerous manifestation but do not have the same pigmentation as malignant melanoma.