u/lazurm

For years I’ve believed that adult thumb sucking is far more common than its near invisibility in everyday life would suggest. Long before there were any good prevalence studies that I knew of, I tried to estimate it myself and eventually settled on a range of about 3% to 7% of adults. But stand by for some real, far more scientifically derived stats, below.

I want to be clear about what my years ago estimate was and wasn’t. It wasn’t “scientific” in the sense of being derived from a properly selected population sample using established research procedures. I approached the problem indirectly.

Among other things, I looked at the number of people who spontaneously admitted to adult thumb sucking in response to total numbers of radio and television program listeners at the time that the program happened to discuss adult thumb sucking. Where audience or visitor numbers were reasonably known, I compared the number of admissions with the proportion of people who ordinarily respond or comment, using the mathematics involved to estimate the range of adult thumb sucking. I also used the total number of visitors to emails and comments admitting their habit and obtained via stats from my website, www.thumbsuckingadults.com . I did this in different circumstances over the years, and the estimates kept falling somewhere around 3% to 7%.

That was enough for me to regard 3% to 7% as a reasonable working estimate, but certainly not enough to call it a scientifically established prevalence rate.

Well, somebody finally did a much better study.

Steffen Moritz and seven other researchers surveyed 1,481 U.S. adults in a diverse online general population sample designed to approximate important U.S. Census demographics. Better yet, participants weren’t recruited by being told that thumb sucking, or even body-focused repetitive behaviors, was the real subject. They were simply told that the survey concerned various psychological experiences. That substantially reduces the obvious problem of attracting people because they happen to have an interest in the behavior being studied.

And here’s the part that made me smile:

4.7% reported current adult thumb sucking.
(Table 1, below.)

That is almost exactly in the middle of the 3% to 7% range I had arrived at years earlier by completely different and admittedly informal means.

“Current” in this study was reasonably inclusive. It ranged from occasional thumb sucking associated with stress through weekly, several times weekly, and daily or almost daily sucking. So 4.7% doesn’t mean that roughly one person in 21 is necessarily sucking a thumb every night. It means approximately one in 21 U.S. adults reported that thumb sucking was still a current behavior at least occasionally.

The researchers classified current thumb sucking as a body-focused repetitive behavior. They also identified a more severe category, called a body-focused repetitive disorder, when the current behavior produced clearly visible or lasting physical consequences.

That second figure was 1.3% of the entire sample. Since 4.7% reported current thumb sucking, dividing 1.3 by 4.7 means that roughly 28% of the current adult thumb suckers fell into the study’s category involving visible or lasting physical consequences. Put the other way around, roughly 72% did not meet that criterion. (Table 1, below.) So much for the general idea that tsing must result in lasting physical consequences, meaning the type of impactful consequences that significantly alter one's abilities. The 28% total doesn't account for the fact that, even without tsing, some would have these results (open bite, proclined upper incisors, etc.) anyway, so the tsing may be even less of a factor than this study may otherwise hint at.

Age makes the findings even more interesting. Among matched samples, 9.1% of adults ages 18 to 39 reported current thumb sucking, compared with 1.7% among everyone age 40 and older. (Table 2, below.)

That 40+ figure needs an important qualification. It combines people in their 40s with people in their 50s, 60s, 70s and beyond. The supplementary data indicate that age 40 is not some magical point at which thumb sucking suddenly disappears. In fact, even the study’s more restrictive body-focused repetitive disorder category remained appreciably present among those ages 40 to 49 before falling sharply in the older groups.

So the most reasonable interpretation seems to be that adult thumb sucking remains meaningfully present through the 40s and then declines with advancing age, although this study doesn’t give us a precise decade by decade prevalence curve for ordinary current thumb sucking.

I’m not claiming that my old 3% to 7% estimate became “proven” because a later, much better study came up with 4.7%. My methods had limitations that a properly designed prevalence study was able to reduce considerably.

But I’ll admit that I find the result pretty satisfying.

For all those years that adult thumb sucking appeared to be an extraordinarily rare behavior, perhaps the real phenomenon wasn’t its rarity at all. Perhaps it was simply extraordinarily good at remaining private.

Table 1. Current thumb sucking in the full U.S. sample, N = 1,481

Measure	Prevalence
Current thumb sucking, classified as a body-focused repetitive behavior	4.7%
Current thumb sucking classified as a body-focused repetitive disorder because of visible or lasting physical consequences	1.3%
Approximate proportion of current thumb suckers meeting that physical-consequence criterion, calculated by dividing 1.3% by 4.7%	28%

Table 2. Current thumb sucking by broad age group, matched samples

Age	Current thumb sucking
18 to 39	9.1%
40 and older	1.7%

Source: Steffen Moritz, Jakob Scheunemann, Lena Jelinek, Danielle Penney, Stella Schmotz, Luca Hoyer, Dominik Grudzień and Adrianna Aleksandrowicz, “Prevalence of body-focused repetitive behaviors in a diverse population sample: rates across age, gender, race and education,” Psychological Medicine. First published online December 13, 2023.