A Long Habit for Some People
Your thumb and fingers are at times your best friend, and for some people, their longest lasting. Many adults continue the practice of thumb or finger sucking from childhood as a safe way to relieve stress in their nervous system. Movies have used the image of someone sucking his or her thumb or fingers to indicate a need for immediate comforting from high stress. This is a symbol everyone understands.
This personal relationship with one's thumb and fingers starts before birth. Ultrasound images of unborn infants often reveal them sucking their thumb or fingers. After birth, thumb or finger sucking is common and aids in soothing and comforting the infant in a way they can control. Most give it up by their first birthday. There is no misalignment to teeth unless continued after the 4th year. After the permanent teeth come in, continued sucking of thumb or fingers may misalign the teeth and distort the pallet.
Some people do continue sucking thumbs or fingers up into adulthood. It is not known why adults still do it. There are no apparent negative physical side effects other than the possible misalignment of teeth, pallet, and jaw bones. Most adults who have the habit say there is no sexual stimulation in it; only personal comforting sensations. Fear of being condemned for the habit is the biggest issue for most people, so the practice is mostly a "closet activity" enjoyed by millions of people worldwide.
What could be so compelling about sucking ones own thumb or fingers? The physiological reason is clear. There are huge numbers of nerve endings in the thumb and fingers that lead directly to the brain. Percentage-wise the surface area of the thumb and fingers is quite small compared to the rest of the body. However, the area of the brain directly affected by these thumb and finger nerves is proportionately much larger than other similar areas of skin. The thumb is directly tied to 4% of the brain and each finger occupies 3% of the brain real estate. It appears that sucking thumb or fingers is one way of reaching directly into one's own brain to stimulate it. Very likely the brain releases comforting and soothing chemicals affecting the whole body through this sucking stimulation.
Compared to other means of soothing and comforting oneself, thumb or finger sucking is relatively harmless and it is free! Go ahead and enjoy it and feel safe in knowing that you are not alone. Your best friend is always there to comfort you.