Function: To protect your body from damage, infection and drying out. Largest organ. Your skin is your largest organ. It covers your entire body and has a surface area of around 2 square metres. Its thickness varies from 0.5mm on your eyelids to 4mm or more on the palms of your hands and the soles of your feet. In total, it accounts for around 16 percent of your body weight. Tough physical barrier.