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Which body system is usually the first to show apparent signs of aging?

From about the age of 25, the integumentary system—the body's largest organ, which includes the skin, hair, and nails—begins to show the first apparent signs of aging. Visible changes like fine lines, a loss of radiance, and changes in texture often debut on the skin's surface before other systems exhibit significant functional decline. This early visibility is due to both intrinsic biological factors and external environmental stressors.