Let's learn together. "Your outer layer of skin, the epidermis (apart from the thicker dermis beneath), replaces itself every 35 days.  You are given a new liver every six weeks (a human liver can regenerate itself completely even if as little as 25% remains of it).  Your stomach lining replaces itself every 4 days, and the stomach cells that come into contact with digesting food are replaced every 5 minutes."