Why do sun spots cause dark patches on skin?

Ultraviolet light stimulates pigment production as part of the skin’s protective response. With repeated exposure, some areas continue to hold more melanin than the surrounding skin. The result is usually a flat, tan-to-brown patch on places that receive sun, such as the face, backs of the hands, shoulders, or chest. The colour may become more noticeable after further sun exposure.

Dark patches have many possible causes, including post-inflammatory pigment, hormonal changes, medicines, and some skin conditions. A new or changing mark should be assessed by its shape, surface, colour pattern, and history rather than labelled from appearance alone.

Use shade, protective clothing, and broad-spectrum sunscreen on exposed skin, applying it as directed and renewing it when needed. Avoid deliberate tanning, because more ultraviolet exposure can deepen existing pigment and encourage additional spots. If a patch is bothersome, a dermatologist can discuss topical medicines, peels, or light-based procedures after confirming the diagnosis. Treatments can irritate skin and may worsen pigment in some people, so professional selection matters.

Book a skin assessment for a spot that is new, rapidly changing, uneven in colour, irregular in outline, bleeding, crusting, painful, or persistently itchy. Also seek review if a patch feels rough or raised rather than flat. These features do not prove a serious cause, but they warrant examination before cosmetic treatment.

Ask whether the patch fits a sun spot, what protection is practical for your routine, whether treatment could irritate your skin tone, and which changes should prompt another examination.