Which of the following is an example of a skin pigmentation disorder?

Lentigo is a skin pigmentation disorder characterized by small, brown spots on the skin that result from an increase in melanin production, often associated with sun exposure. These spots can appear on areas of the skin that have been exposed to the sun over time and are not harmful, though some patients may seek treatment for cosmetic reasons. The term "lentigo" specifically refers to these pigmented lesions, making it a clear representation of pigmentation disorders.

Other conditions like eczema, psoriasis, and alopecia are primarily inflammatory or autoimmune disorders that affect the skin's appearance or health but do not directly involve changes in pigmentation itself. Eczema involves inflammation and can lead to red, itchy patches; psoriasis is characterized by rapid skin cell turnover, resulting in scaly plaques; and alopecia specifically pertains to hair loss without affecting skin pigmentation. Thus, lentigo stands out as the example that accurately represents a skin pigmentation disorder.