The science of toilet training: What research tells us about timing

When is the best time to start teaching children about toileting? Infancy? 18 months? 24 months? Or even later? What does the science of toilet training tell us?

There is surprisingly little research addressing the question. And, as I note elsewhere, each age is associated with its own costs and benefits. But three points seem clear.

  1. It’s possible to begin toilet train very early in life — if you use methods that are safe and developmentally-appropriate.
  2. Younger children may take longer to master toilet training skills, so if you start relatively early (e.g., before 24 months), your child may may require a longer duration of training.
  3. Based on existing studies, more medical problems have been linked with initiating training later (after 24 months) than earlier (before 24 months). 

For the details, read on.

baby peaking through stacks of diapers

Studies suggest that infant toilet training — practiced safely and correctly — might protect kids from the development of bowel and bladder problems.

In many parts of the non-Western  world, it’s traditional for children to begin toilet training during infancy. How does this work? You can read the details in this Parenting Science article, but the quick version is this: Families learn to communicate successfully about the timing of elimination. When a baby needs to void, the parent holds the infant over an appropriate receptacle, and gives the signal for the baby to proceed.

Does this practice — called “elimination communication” — cause harm? That seems unlikely. In fact, studies suggest that infant training reduces a child’s risk of developing long-term bladder and bowel problems.

For example, consider China, where elimination communication is the norm. In a sample of more than 10,000 kids (aged 4-10 years), researchers there found that rates of bladder and bowel dysfunction were lowest for children who had started infant training before 12 months (Xu et al 2021). A similarly large study reports that that children who began traditional training prior to 12 months were less likely to develop overactive bladder later in life (Xing et al 2020).

There is also an alternative, potty-chair based approach to infant training — one that can be attempted after a baby has learned to sit up on his or her own.  It, too,  depends on realistic, gentle, age-appropriate methods. You can read more about it here. Does this sort of training cause problems? I haven’t found any systematic, scientific tests of this approach. But when investigators monitored the progress of infants in a small clinical study, they observed no adverse side effects (Smeets et al 1985).

Studies also hint that it’s beneficial to begin toilet training before a child is 24 months old.

From the standpoint of avoiding medical problems, is it better to start training a toddler before he or she is 2 years old? Or should you wait?

Recently, researchers analyzed the best evidence available — 10 different published studies, addressing a total study population of more than 24,000 children — and the trend was clear. Kids who began training before 24 months tended to enjoy better long-term health outcomes.

It didn’t matter if they had started out as young infants using elimination communication, or if waited until they were a bit older and begun with an age-appropriate, potty chair training method. Either way — as long as they had initiated training before 24 months — they were less likely to have developed urinary tract problems (Li et al 2020).

Do all studies say the same thing? No. I’ve found at least one piece of counter-evidence. In a study of 112 children, kids referred to a urologic clinic for voiding dysfunction were more likely than symptom-free kids to have been trained either before 24 months or after 35 months (Hodges et al 2014). But the overall pattern — across studies — supports the idea that early trainees have a lower risk of urinary tract troubles.

That doesn’t mean that there’s no downside to early training. It can be a lot of work for parents, and kids who start younger might take longer to achieve toileting independence.

The work is especially evident for elimination communication. Parents must be ever-vigilant and “tuned-in” to their infants’ needs. But toddler training — using a potty chair — comes with its own challenges. For instance, some toddlers may try to suppress the urge to eliminate in order to avoid a tedious visit to the bathroom. But it’s an unhealthy habit — one that can lead to constipation and urinary tract problems — so parents need to stay alert and encourage kids to use the potty many times each day.

It’s also worth considering: Starting earlier might mean your child will take a bit longer to complete training. Older kids have more motor skills, and these skills help them speed through the training process. For example, kids who are capable of pulling their own pants up and down may go into potty training with an advantage (Wyndaele et al 2020). And at least one study suggests that younger toddlers need more time to learn.

In this study, Nathan Blum and his colleagues tracked more than 400 American children from the age of 17-19 months, checking in with parents every 2-3 months until their kids had completed daytime potty training. Training was considered “complete” when children were wearing underpants rather than diapers, and experiencing a maximum of 3 urinary accidents and 2 fecal accidents per week (Blum et al 2003).

The researchers were particularly interested in the duration of “intensive” potty training, the sort of training that includes having your parent ask you to sit on a potty chair at least 3 times per day. They also wondered if age at initiation made a difference, so they compared two groups — kids who had started intense training before 27 months, and kids who began intensive training after 27 months.

And the outcome? Both groups were equally likely to have encountered problems along the way — problems like constipation, stool toileting refusal, stool withholding, or hiding from parents. But children trained earlier tended to take longer to complete training. Kids who starting training between 18-24 months took, on average, 13-14 months. Kids who trained after 27 months took 10 months or less (Blum et al 2003).

What if you wait longer, until your child is nearly three years old — or even older?

As we’ve already noted, starting toilet training anytime after 24 months has been linked with higher rates of urinary tract dysfunction. And the evidence includes studies with large sample sizes, like one that one that tracked long-term outcomes in more than 8500 kids (Joinson et al 2019). But does the risk keep getting higher as children get older?

Studies haven’t really addressed this point. We need more research. But there are theoretical reasons to suspect that earlier training could be beneficial. When we urinate, it’s important to eliminate all fluid from the bladder. It reduces the risk of developing urinary tract infections. And toilet training? It helps kids learn how to completely empty the bladder.

So the earlier children begin toilet training, the earlier they develop this healthy habit (Janson et al 2000; Sillen and Hanson 2000). And the difference may be pretty dramatic.

In a cross-cultural study, researchers measured the voiding patterns of children living in Vietnam and Sweden. Most of the Vietnamese children had begun toilet training before the age of 6 months, and by 9 months, they had mastered the art of bladder-emptying: After an act of urination, their bladders were completely free of any residual urine.

By contrast, 95% of the Swedish kids hadn’t even started training by the age of 24 months, and these children didn’t achieve complete emptying until they were 36 months old (Duong et al 2013).

Does the timing of toilet training have any psychological effects?

Yes, but the crucial factor isn’t the child’s chronological age. Instead, what’s important is that you choose a time when your child is healthy (free of any urinary tract or bowel troubles) and ready to cooperate. And of course you must make sure that your goals and methods match your child’s developmental capabilities. Regardless of your child’s age, you want to make the process friendly and cooperative — not pressured or coercive. Punishments — for accidents or non-compliance — are always a bad idea.

But wait, you might ask. I’ve heard that early toilet training causes psychological problems. Isn’t this true?

It’s true that some people have made these claims. But it’s helpful to understand the historical context. I suspect that early potty training got a bad reputation because it was once associated with harsh or coercive training methods.

In the 1920s and 1930s, parents were urged to impose a rigid toilet training regimen on children before they could walk. Techniques were coercive — sometimes even abusive.

One government manual instructed parents to enforce “absolute regularity” of bowel movements by inserting a soap stick in the infant’s rectum at precise times of the day (United States Department of Labor 1935). Other prevalent tactics included scolding and physical punishments for accidents (Hushka 1942; Stendler 1950; Luxem and Christophersen 1994.)

After World War II, the medical establishment began to reject early potty training. Freudian psychologists argued that early, rigid training caused emotional problems and neuroses later in life. And pediatricians, like Benjamin Spock and T. Berry Brazelton, warned that pressuring children may cause a variety of troubles, including stool withholding, stool toileting refusal, regression, and bed-wetting (Leiberman 1972; Brazelton 1962; Brazelton and Sparrow 2004).

So some child development researchers adopted the idea that training should not begin until kids could actively cooperate with the process (Brazelton et al 1999). Strict timetables for training were abandoned. Instead, parents were encouraged to let their children’s spontaneous curiosity set the pace.

These changes probably saved many children from harsh training methods. But it seems to me that reformers made the mistake of confusing methods with timing. For instance, in one historical study I’ve read, the author states that that any training before 10 months is, by definition, coercive (Hushka 1942).

What about this Freudian notion that toilet training causes psychological problems? It’s interesting to note that Freud himself never singled out early training as the cause of personality disorders. He was concerned about any approach to training that might be regarded as extreme—too early, too late, too strict, too “libidinous” (Fenichel 1945, p. 305).

And in any case, I can find no scientific studies that link the age of toilet training initiation with the later development of emotional disorders. Freud identified certain personality types that have been confirmed by modern scientific studies. However, these personality types have NOT been linked to childhood toilet training experiences (Fisher and Greenberg 1977; Masling 1999).

More information

For more information, be sure to check out my article on choosing the right potty training age, as well as these evidence-based potty training tips.

References: The science of toilet training

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Written content of “The Science of toilet training: What research tells us about timing” last updated 10/2021

image of baby peaking through stacks of diapers by istock / ysuel