While you may think the largest organ in the human body is the liver or heart, it is in fact the skin. As well as being the largest, it is also the body’s only external organ, meaning it functions as a unique barrier to protect your internal organs from damage and attack. In fact, on the average adult, the skin accounts for roughly 16% of our body weight, covers a total surface area of around two square metres, and contains more than 17 kilometres of blood vessels.