Which of the following is a primary cause of external effects on the skin?

• A. Genetic factors
• B. Pollution exposure
• C. Sun exposure
• D. Misuse of products

Answer: (D)

Sun exposure is the primary external factor that affects the skin. UV radiation from the sun damages skin cells directly and indirectly: UVB causes DNA damage and burns, while UVA penetrates deeper to generate free radicals that break down collagen and elastin, leading to aging, pigment changes, and higher cancer risk. Other environmental factors like pollution can add to skin stress, but the sun's rays are the dominant external driver of long‑term skin damage. Internal factors such as genetics influence skin from within, and misuse of products may irritate the skin, but it does not represent the main external cause of widespread skin effects.