Keratins are a group of tough, fibrous proteins that help maintain healthy joints and support skin, hair and nails. Keratins deliver an exceptionally high content of the amino acid cysteine, which is in itself an abundant source of sulfur molecules that nourish and strengthen cartilage tissues. When the sulfur molecules from cysteine bond together they form very strong links called "cysteine bridges." These bridges provide vital support for weight-bearing joints. New Swanson Premium Brand® Keratin, derived from Tibetan wool, supplies pure, food-grade hydrolyzed keratin to nourish healthy connective tissues and promote the health, strength and appearance of skin, hair and nails.