Chondroitin is a vital part of cartilage, giving it elasticity by helping it retain water. Chondroitin helps to prevent the breakdown of collagen in the joints and decreases the effects of wear and tear on the joints.(Chondroitin sulfate comes either from animal sources such as shark or cow cartilage or is made in a lab, so it is not a shellfish extract (as glucosamine is), but if anyone does have a shellfish allergy and they have any reaction such as hives or itching, best to stop using the product and consult a doctor).