Which condition is described as small brown spots that appear due to sun exposure and are often considered a sign of aging?

The condition characterized by small brown spots that develop due to sun exposure and are commonly perceived as a sign of aging is lentigo. Lentigines, often referred to as age spots or liver spots, are flat, tan, brown, or black spots that typically appear on sun-exposed areas of the skin. These spots result from the increased production of melanin, the pigment responsible for skin color, as a protective response to UV radiation from the sun.

Recognizing lentigo as a sign of aging stems from the fact that their prevalence increases with age, as cumulative sun exposure over the years leads to more pronounced pigmentation changes in the skin. This differentiates lentigo from other conditions, such as naevae, which refer to moles that are typically congenital and not solely related to sun exposure, and ephelides, which are usually lighter freckles that tend to fade in the winter months and are more associated with genetics than aging. Vitiligo, on the other hand, is a condition that causes loss of skin pigment and results in white patches rather than the brown spots associated with lentigo. Therefore, lentigo specifically aligns with the description provided in the question regarding sun exposure and aging.