What causes the skin to appear flat or discolored?

The appearance of flat or discolored skin is typically associated with maculae. A macula is a term used in dermatology to describe a small, flat area of discoloration on the skin that is not raised above the surface. This can occur due to various reasons, such as changes in pigmentation, vascular lesions, or other skin conditions. The flat nature of maculae means they do not have texture and are often distinguished by differences in color compared to the surrounding skin, which could indicate conditions like freckles, age spots, or post-inflammatory hyperpigmentation.

Other conditions listed, while related to the skin, do not specifically describe flat discolorations. For instance, fissures refer to deep cracks or splits in the skin, milia are small cysts that appear as raised white bumps, and a nevus (or mole) typically has a raised texture, being a proliferation of melanocytes. Thus, the definition and characteristics of maculae make it the correct choice for describing a skin appearance that is flat and discolored.