Lips are among the most flexible parts of the human body. They can be moved upward, downward, sideways, front and back, outward and inward, in strange patterns and the upper and lower lips can be moved in dynamically different sides, directions and patterns. The muscles in the lips are very subtle and soft yet well controlled. A normal human being will be able to make dozens of different kinds of motions with his or her lips. Naturally, lips form a core part of behavioral science and especially the subject of body language.
There are many kinds of motions that people typically indulge in with their lips. For instance, people part their lips, purse and pucker them, suck them in or flatten them, turn them up and down and retract them, move or twitch and protrude them as well as relax and bite them. Many of these motions or actions are voluntary but all of them can be involuntary as well, depending on the situation a person is in and the natural behavioral or body language of a person.
The act of biting bottom lip is most common among kids but adults are also not immune to this pseudo-voluntary act of trying to conceal something, being anxious, feeling embarrassed or being reprimanded. Those who have a habit of biting bottom lip may bite the lower lip at the side or around the center region. They are not as likely to bite the upper lip because that takes more effort, considering that lower jaws are more confined within the upper jaws, and seldom is the upper jaw docketed in the lower jaw and thus the upper lip inside the ambit of the lower lip.
Kids bite their bottom lips when they are afraid of telling the truth, when they wish to tell a lie, want to say nothing, are afraid and are being reprimanded. When a child has done something that he or she was told specifically not to do, he or she would bite the lower lip.
Adults bite their bottom lips when they are nervous and often spellbound. When they don’t know what to say or what to do and especially when they are with people who are superior to them in any way, it is the most natural scenario to bite the lower lip.
The act of biting lower lip can be voluntary or involuntary. It varies from one person to another.