Skin Has a Brain

Your skin does more than report sensations — it runs chemistry of its own. Skin cells can make signaling molecules like serotonin and melatonin and can release stress hormones, so the surface reacts to sunlight and stress partly on its own, before your brain weighs in.

It is also packed with touch sensors, and not evenly. Your fingertips and lips carry far more than your back, which is why you can feel a single grain of sand on a fingertip but barely notice the same grain between your shoulder blades.