What causes humans to be ticklish?

When the nerve endings in your epidermis are stimulated, they engage two different parts of the brain – one that analyzes touch and another that regulates pleasurable feelings. Furthermore, when we laugh as a result of our tickle reflex, the hypothalamus kicks into action and launches the fight or flight response. The sensitive areas of our body that are commonly ticklish are also the most vulnerable to attack and the least protected (e.g., bottom of the feet, armpits, rib cage). Therefore, when they are stimulated, the instinctive laughter may act as a natural sign of submission to one’s attacker, which may cause the unpleasant stimulation to cease