What are small flat macules of brown melanin that occur on sun-exposed skin known as?

The correct term for small flat macules of brown melanin that appear on sun-exposed skin is called ephelides, more commonly known as freckles. Freckles are small, harmless spots that typically develop due to an increase in melanin production in response to sun exposure. They are often seen more prominently in individuals with lighter skin tones and usually tend to darken in the summer when exposed to more sunlight.

Lentigo, on the other hand, refers to a larger, more defined brown spot that is also related to sun exposure but is typically more prominent than freckles and may appear as a result of aging or sun damage. Naevae (the plural of nevus) refers to moles, which are generally raised and can be either brown or flesh-colored, quite distinct from the flat nature of freckles. Chloasma, also known as melasma or the "mask of pregnancy," involves larger patches of brown pigmentation that often occur on the face due to hormonal changes rather than solely from sun exposure.

Understanding these distinctions helps in recognizing how different pigmentation marks are classified based on their appearance, location, and the underlying causes of their formation.