Is It "Normal" to Suck Your Thumb?

by Katherine Dettwyler, PhD

Department of Anthropology,
Texas A and M University

This was originally sent in a note to LACTNET in response to a doctor suggesting that all children should be encouraged to suck their thumbs.

Dear LactNetters,

I wrote this in response to an e-mail from a doctor in Switzerland (not our friend Jim Akre from WHO) who took offense at my statement in my chapter on weaning from the book that it wasn't normal/natural for human children to suck their thumbs or fingers, and that such behavior was a sign of a child whose needs weren't being met at the breast. He countered that self-comforting was a good talent for infants/children, and that even fetuses in the womb sucked their thumbs. When I finished writing this I decided maybe you'all would like to read it.

Re the thumb-sucking issue -- it is certainly true that ultrasound and photography in the womb shows fetuses sucking their thumbs, but then breasts/nipples aren't available in the womb, but the suckling instinct is clearly present from an early age. Once the baby is born, however, the suckling instinct is supposed to be directed toward the breast, to get the child nutrition and immunities, and the sucking itself lowers the baby's heart rate and blood pressure. While it can be convenient for the parents to have the baby suck on their thumb or fingers or pacifier (like in the car on trips, or when mother is trying to cook dinner) it nevertheless is clear from both cross-cultural and cross-species field studies that, given complete contact with mother and free access to the breast on demand, human children (and young of our close relatives, the great apes) do not suck on their thumbs or fingers. I never saw a child in Mali sucking its thumb or fingers, in almost three years of watching/observing/studying mother-child interactions. Likewise, thumb sucking is reported to be completely absent from cultures such as the Navajo, in highland Papua New Guinea, Ecuador, the Peruvian Andes, Mexico, Nepal, India, Tanzania, Botswana, and South Africa. A number of other ethnographic studies of breastfeeding don't mention thumb sucking one way or another.

Thumb sucking is also absent from the great apes (chimpanzees and gorillas) except among zoo nusery raised animals.

I think it is clear that human children have sucking instincts that can persist until 7 or 8 years of age, or even longer, and must meet those needs somehow -- through thumb, finger, or pacifier, if not allowed to meet them at the breast. But I also think that meeting those needs at the breast is the "normal/natural" context or situation, and involves not just lowering the heart rate/blood pressure, but also the transfer of nutrients and immunities, as well as helping the child with thermoregulation from being in contact with its mother's body. It may be that thumb/finger/pacifier sucking "tricks" the child into being "pacified" for the time being, even to the extent of reducing the time spent at the breast. That doesn't mean it is good for the child. In fact, finger and thumb sucking often lead to orthodontic problems. In the U.S. orthodontists even have evil-looking devices they will install in a child's mouth to make it painful for the child to continue sucking their thumb/fingers, in order to break them of this habit. If the child were allowed to meet those sucking needs at the breast, it wouldn't lead to orthodontic problems (in fact, just the opposite, with less orthodontic problems in long-term breastfed kids).

Any time you force the child to rely on their own resources prematurely, you must expect deleterious consequences. When the child's needs are met through person-to-person interaction with its mother, you establish the primacy of social contact, and the interdependence of human beings, rather than encouraging/forcing the child to meet its needs by itself.

This may be a crude analogy, but consider this: If you have two adults, married to each other, who have all the children they want and don't want to get pregnant, but still have strong sex drives, would you consider it better if they each went into a separate room and masturbated? This would certainly allow them to "self comfort" and would make them independent and autonomous, so that one wouldn't have to wait until the other was ready or "in the mood." Would you really consider this an improvement?

[The next section was written a few days later, after a number of people expressed disagreement.]

More thoughts on thumbsucking:

Of course all babies are different, and some develop the habit of sucking their thumbs in utero, and moms don't think anything of it, so it continues. Evidence based on cross-cultural research and analysis of human breast milk content suggests that human babies are designed to nurse *several times an hour* around the clock. One would expect that their has been selection for a strong instinct to suck in this pattern, and nursing *on demand* can be altered significantly by the mother, who of course has other things to do. I'm not suggesting that all babies must be held continuously by the mother with continuous access to the breast -- just that that is what they have evolved to expect, and their sucking instincts have evolved accordingly. When you look at mothers who say they are nursing *on demand* but the baby only *demands* every 3-4 hours, you usually find subtle and not-so-subtle messages from the mother that nursing more often is not allowed. Thus, baby may turn to his thumb or fingers, and since mom thinks "baby can't be hungry again" she lets him pacify himself.

My own research suggests that the absolute minimum time human children have evolved to expect breastfeeding to continue is 2.5 years, with a range of 2.5 to 7 years. Thus, one would expect that for many of them, their sucking instincts will remain strong throughout this period, and thus one would expect a child nursed for 2 years to be very likely to still have the instinctive urge to suck til 6, 7, 8 years or even longer. I strongly encourage parents of thumb-suckers to let their children suck their thumbs (fingers, pacifiers) as long as they need to.

I was responding to a Swiss doctors claim that all children should be *encouraged* to suck their thumbs to make them more independent of their mothers as early as possible. He was saying that self-comforting is better than comforting at the breast. I disagree. That's all.

Prepared  November 28, 1995. Updated November 30, 1995.

Last updated September 23, 1999, by sak. Contents copyright 1999 Sue Ann Kendall and Kathy Dettwyler.   Thanks to Prairienet, the Free-Net of east-central Illinois, for hosting this site.

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