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Nails are protective plates found at the tips of fingers and toes in almost all primates, made of a tough protein called alpha-keratin—the same material found in claws, hooves, and horns. The nail's structure includes the nail matrix (the active tissue that generates new cells), the nail plate (the visible, translucent hard part), and the nail bed (the skin beneath it, which is highly innervated, making nail removal extremely painful). The pinkish color of nails comes from capillaries in the nail bed showing through the translucent plate, while the whitish crescent at the base, called the lunula, is the visible part of the matrix. The shape of the nail plate is determined by the underlying bone, and the matrix continues producing cells as long as it stays healthy, pushing older cells forward to become flat and translucent. At the free edge, the hyponychium (or "quick") forms a protective seal, and together the eponychium and cuticle shield the base of the nail from infection.