Your baby sucks their thumb because sucking soothes them: it's a reflex present from birth, not a bad habit. Before 18 months, there's nothing to correct. The question of teeth only comes up later, and most children stop on their own at around 3 or 4 years old.
Thumb sucking often worries parents, because we tend to link it with teeth pushing forward and comments from family and friends. Yet public health sources are reassuring about the early years. Here's what we know, age by age, and how to support your child in stopping when the time comes.
Why babies suck their thumb
All newborns have a sucking reflex, notes the Institut national de santé publique du Québec (INSPQ), Quebec's public health institute. Sucking is first and foremost for feeding. It also helps babies calm down, even when they aren't hungry.
The thumb has one advantage over any other object: it's always there. Your child finds it alone, without an adult's help. The US medical library MedlinePlus sums it up like this: thumb sucking can help a child feel secure and happy.
When they reach for it
- when falling asleep, at bedtime as well as at nap time;
- when they're tired or hungry;
- when they're bored;
- when they're stressed, upset or somewhere unfamiliar.
These situations have one thing in common: your child needs to bring the tension down. The thumb then plays the same role as a comforter, a transitional object that reassures them when their parents aren't close by.
At what age do babies find their thumb?
A newborn first sucks whatever touches their lips. Deliberately discovering their hands comes later. At around 2 months, babies open their hands from time to time, according to the milestones of the US Centers for Disease Control and Prevention (CDC).
At around 4 months, the CDC says most babies bring their hands to their mouth. At the same age, they look at their hands with interest. Some find their thumb at this point, while others prefer two fingers, the whole fist or a corner of fabric.
This oral exploration is part of normal development. It carries on with objects, as explained in our article on why babies put everything in their mouth. Floor time on a play mat leaves their hands free to move and find their way to their mouth.
Does thumb sucking damage teeth?
Not in early childhood. The sources agree on this point, but differ on the age at which it becomes something to think about.
- The INSPQ states that after 18 months, sucking a thumb or fingers can affect how the jaws and teeth develop. It cites the Canadian Paediatric Society (Société canadienne de pédiatrie), which recommends stopping before age 3 to 4.
- MedlinePlus considers it acceptable for a child to suck their thumb until the permanent teeth come through, at around age 6. It does, however, advise helping the child stop at around age 4 to prevent damage.
These two positions don't contradict each other on the essentials. Before 18 months, there's no reason to step in. Between 2 and 4 years, you simply observe, without making a drama of it. Beyond age 4, it's worth raising the subject with your child and, if needed, with the dentist.
What makes the effect on the mouth worse
According to MedlinePlus, damage to the teeth or palate seems more common in children who suck hard. Duration matters too: a thumb sucked for a few minutes while falling asleep doesn't have the same effect as a thumb kept in the mouth all day.
Good hygiene habits stay the same, thumb or no thumb. Our article on brushing your baby's teeth covers the official recommendations from the very first tooth.
Thumb or dummy: should you swap one for the other?
Some parents offer a dummy to a baby who sucks their thumb a lot. The INSPQ notes that a dummy is often easier to control: you can take it away, whereas the thumb is always within reach.
That doesn't make it free of drawbacks. The INSPQ points out that the risks to teeth are the same after 18 months. It adds that after 12 months, a dummy can increase the risk of ear infections. Our guide to choosing a dummy goes through shape, size and safety rules in detail.
There's no obligation to replace the thumb. A baby who soothes themselves with their thumb doesn't need an extra object. The choice depends above all on what suits your child and your family.
How to help your child stop when the time comes
Stopping is something to prepare for at around age 4, rarely earlier. MedlinePlus suggests several gentle approaches, all based on the same principle: understand why your child sucks their thumb, then meet that need in another way.
- Offer a toy or a soft toy when they reach for their thumb out of boredom.
- Bring nap time or bedtime forward at the first signs of tiredness.
- Help them put their frustration into words rather than turning to their thumb.
- Praise them when they manage without it, without making a big deal of it.
- Ask the dentist or doctor to talk to them about it: children often listen better to someone else.
If the thumb is red or chapped from all the sucking, a barrier cream can soothe the skin. Aids such as a thumb guard, a bitter-tasting nail varnish or a dental appliance should be discussed with a professional, and only for older children.
What's best avoided
MedlinePlus is clear: don't punish your child or nag them to stop. A child under pressure may suck their thumb even more, since the thumb is precisely what helps them bring the tension down. Teasing from family and friends can have the same effect.
With a toddler, there's no stopping to organise. A thumb kept for falling asleep needs no intervention at all.
When should you talk to a professional?
Thumb sucking in itself doesn't call for an appointment in a toddler. It's worth mentioning to your doctor, midwife or dentist in a few situations:
- your child sucks their thumb so much that the skin on the finger is damaged;
- the sucking doesn't decrease at all after age 4;
- the teeth or the shape of the mouth seem to be changing;
- the thumb sucking seems linked to strong anxiety or a sudden change in behaviour.
Your child's regular check-ups are also a good chance to bring it up, without waiting for a problem.
Key takeaways
- Thumb sucking is a normal reflex that soothes your child; there's nothing to correct before 18 months.
- At around 4 months, most babies bring their hands to their mouth, and some find their thumb.
- Most children stop on their own at around 3 or 4 years old.
- After 18 months, prolonged sucking can affect the teeth; the Canadian Paediatric Society advises stopping before age 3 to 4.
- Stopping is best supported gently, without punishment or teasing.
Sources
- INSPQ, “Succion et utilisation de la suce”, Mieux vivre avec notre enfant de la grossesse à 2 ans, updated 17 February 2026.
- MedlinePlus (National Library of Medicine), “Thumb sucking”, reviewed 1 July 2025, by Neil K. Kaneshiro, MD.
- CDC, “Important Milestones: Your Baby By Four Months”, Learn the Signs. Act Early, updated 16 May 2026.
- CDC, “Important Milestones: Your Baby By Two Months”, Learn the Signs. Act Early, updated 16 May 2026.
