When you touch something, you detect it using mechanoreceptors just below the surface of your skin. These send the information to your brain. How close can two pinpoint touches be before you sense them as just one touch? It varies over the surface of your body, from 2 millimetres on your fingertips to 40 millimetres on your forearms. The parts of your skin that need to be most sensitive, like your fingertips and your lips, have more receptor cells in them than other, less sensitive areas.