Solar keratosis (also known as actinic keratosis or senile keratosis) is a common precancerous skin lesion caused by long-term, cumulative exposure to ultraviolet (UV) radiation from the sun or tanning beds, leading to abnormal keratinocyte growth in the epidermis. It typically appears as rough, scaly, dry patches or small crusty bumps on sun-exposed areas such as the face, scalp (especially bald spots), ears, lips, neck, backs of hands, forearms, or upper chest. The lesions are usually 2–10 mm in size, vary in color from flesh-toned to red, brown, or tan, feel sandpaper-like or like a small wart, and may be slightly raised with a white or yellowish scale; some are flat and barely visible except to touch, while others can be itchy, tender, sting, or occasionally bleed if picked. They are most frequent in fair-skinned older adults with a history of significant sun exposure, and while many remain stable, a small percentage (estimated 5–10% over years) can progress to squamous cell carcinoma if untreated.