An enzyme that breaks down a substance in the body called hyaluronic acid. Hyaluronic acid is found throughout the body in connective tissue, skin, and fluids in the joints and inside the eye. It causes fluids to have a jelly-like thickness, which can help moisten and protect tissues and joints. In medicine, hyaluronidase is made in the laboratory and given with other drugs by injection under the skin to treat certain conditions. Using hyaluronidase to break down hyaluronic acid helps make the fluids and connective tissue thinner so the drugs can move more easily into the tissues.