How to distinguish between senile lentigines, melasma, and flat warts

Senile lentigines, melasma, and flat warts differ明显 in several aspects. Key points for differentiation: 1. Morphological characteristics: Senile lentigines are often irregular in shape, with uneven surfaces, blurred borders, and uneven coloration; melasma typically appears symmetrically on the face, such as on the cheeks, forehead, and around the mouth, with a butterfly-like shape, varying in color from light grayish brown to dark brown; flat warts are mostly round or oval, with smooth surfaces, clear borders, and colors usually matching normal skin tone or light brown. 2. Age and location: Senile lentigines primarily occur in middle-aged and elderly individuals, commonly developing on sun-exposed areas such as the face, forearms, and back of the hands; melasma also commonly affects adults but has no specific age restriction and mainly impacts the face; flat warts tend to occur in young and middle-aged individuals and frequently appear on exposed areas such as the back of the hands, fingers, face, and forearms. 3. Etiology: Senile lentigines are mainly caused by long-term sun exposure; melasma has a complex etiology and may be related to multiple factors such as endocrine changes and ultraviolet radiation; flat warts are caused by infection with the human papillomavirus (HPV).