There are several types of tickling. A gentle tickling (such as with a feather or fingertips) is called knismesis, and an intense form with the use of force is called gargalesis.
Tickling is caused by the body's response to the world around it. Already from the cradle, the baby begins to learn his own emotions. As a rule, external influence on the skin becomes one of the first sensations in his life. Very often, those children who were little tickled in childhood become sullen and withdrawn in themselves. Gentle or light tickling is accompanied by pleasant sensations when touched, the skin becomes covered with "goose bumps". Intense tickling results in loud laughter, squeals, hysterical laughter, etc. This is due to the fact that at first touching scares people, and after that the brain gives a signal that there is no danger. Studies have shown that self-tickling does not give such a result, for the reason that the nervous system accurately recognizes the source of "danger". Thus, in this case, the body simply ignores any actions in relation to it. Another reason that a person is afraid of tickling is the huge number of nerve endings that send signals to the brain. The most sensitive areas are the feet, armpits, neck, back, ears, genitals. It is believed that those people who are afraid of tickling are jealous enough in a relationship. This hypothesis has no scientific confirmation, although there is a connection between a person's behavior towards his beloved (beloved) and the degree of sensitivity from touch. It is recommended to laugh more often from tickling for those who want to lose weight. Of course, the results are not as visible as with vigorous exercise. The average number of daily calories burned from ten minutes of laughter ranges from ten to forty. For a person, this kind of irritation of nerve endings is not only a way to increase mood and sexual arousal, but also is used as a punishment. That is, people are subjected to "delicate" torture, which is rather difficult to survive without harming the psychological state of the person.