Have you ever noticed the leather bag that you carry with all the stuff under the sun? It gets so stretched that it reaches the limit of its elasticity. It is then, when you see those wrinkle type marks on your old overused leather bag.
You discard it and buy a new one. But you cannot do this with your own skin! Yes, your skin is composed of elastin which can be thought of as a soft elastic tissue. It is soft, supple and stretchable but it too has its own limits. Some situations exert extra pressure on your skin such as sudden weight gain or loss, pregnancy and even rapid growth of your body during teenage. Sometimes while exercising too, you stretch your body out of its limits. In such situations you get those thick red or purple lines on your skin which is popularly known as stretch marks.