Collagen is found in your skin, bones, muscles, nails, ligaments, tendons and hair. In fact, it makes up about 25% of the human body's protein. In addition to providing strength to many of the body's tissues, it's also part of what makes skin look youthful and healthy. As you age, the body's collagen production naturally slows. After the age of 25, it starts dropping off at a rate of nearly 2% per year. This slowdown in collagen production will start to have an effect on the skin. You will start to notice more wrinkles and fine lines. Plus, you may notice that you tend to have more injuries and aching joints.