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Does on demand breastfeeding at night cause dental decay?

Katie Davis - January 2020. 5 minute read. 

I don’t know

A friend, who also happens to be a mother and a dentist asked me a while back if she thought she needed to brush her 10-month-olds teeth after his last breastfeed at night to stop him getting dental decay. It was a good question, but I didn’t know the answer.

Would you wake up a sleeping baby to brush their teeth after the last feed? (surely this is crazy, right?) Do you brush after each still feed in the night? (again, level 10 madness) Can breast milk cause dental decay? (So, I feel uncomfortable about this question and I don’t know why?)

We sat in our staff room, and realised, that despite being parents AND dentists, we were ill-equipped to answer these questions. 

How do you get dental decay?

To get decay you need all 4 of these factors. 
Bacteria exist in babies mouths (Streptococcus mutans is the one that causes decay)
Sugar breast milk contains lactose, which is a sugar. 
Time boobs are usually in babies mouths quite often right?
Therefore, once teeth have arrived breastfeeding should cause decay right? 
Surely not? Surely evolution cannot have got this so WRONG.

Back to boobs, what did I learn at dental school about breastfeeding?

At dental school, I was taught a shamefully small amount about breastfeeding. I was taught that breastfeeding is the best source of nutrition for a baby, and they should be breastfed until 6 months. I was taught that at this point the first baby tooth comes through, and this is when the baby will be “naturally displaced” from the breast due to the presence of teeth. (That’s it, that is all I learnt at dental school!)Until recently hadn’t given breastfeeding much thought (Justina and I met when her son was 4 & they was past breastfeeding, and it never came up in conversation).

So, in true Katie Dentist fashion, I decided to do some research and spoke to some experts. 

As a Dentist what guidance is available? 

Honestly, I am a little bit embarrassed to say this. There is very little guidance on how to manage baby teeth and on-demand night breastfeeding past the age of 12 months in relation to dental decay. Recent systematic reviews highlight shortcomings in existing studies as confounding factors cannot be controlled (confounding factors, in this case, are toothbrushing, fluoride use, and intake of sugary drinks and foods, which will all impact the chances of getting decay) and therefore conclusions cannot be drawn (2). 

This makes the advice to continue on-demand breastfeeding to 2 years and beyond from The World Health Organisation, just a tad confusing for both parents and professionals. This means, when you ask your dentist, nurse or doctor for advice we are basically just guessing.

Breastfeeding is magic 

There is a crapload of solid evidence about breastfeeding in general, and it’s many health benefits to both Mum and Baby. Unicef states that the benefits of breastfeeding include;

Infant health: It protects children from a vast range of illnesses including infection, diabetes, asthma, heart disease and obesity, as well as cot death (Sudden Infant Death Syndrome).
Maternal health: It also protects mothers from breast and ovarian cancers and heart disease.
There is even evidence that breastfeeding to the age of 12 months actually reduces the chances of dental decay! (3)(more confusion, teeth arrive at 6 months, what changes after 12 months?)

This is why professionals are encouraged to support mothers to choose to breastfeed if they are able to. Well, this all sounds bloody wonderful, right? 

So, what’s the problem? 

Brace yourself. Very occasionally (and we are not 100% sure why because we don’t have the evidence yet) it seems, some children will get decay from on-demand night time breastfeeding over the age of 12 months.

What does it look like? (click here if you're not squeamish)

Bottle/baby or nursing caries is a form of tooth decay that is caused by children sleeping with bottles, (and as mentioned reluctantly above, rarely by on-demand night time breastfeeding). It is more commonly caused when a child goes to bed with a bottle filled with milk or juice-anything except cooled, boiled water. The decay forms in a very particular pattern, all teeth except the lower front ones.

Boob Vs. Bottle
Feeding from a bottle isn’t the same as feeding from the boob. 
Most of the time, night time feeding from a bottle will cause bottle caries
Very rarely breastfeeding on demand will cause nursing caries. 

I’m going to be real practical about this because breastfeeding is truly wonderful. It is the most magical thing I think we can do as humans (sorry fellas). Stay with me here….

Why breastfeeding doesn’t cause decay in the majority of babies.

Let’s go back a few years….

Humans have been around in our modern form for around 100,000 years.
Dental decay developed around 8,000-10,000 years ago. (What has changed? We don’t actually know!)
There are 4640 species of mammals, humans are only one of these.
All species breastfeed their young (most, not all have lactose in their milk), only humans get dental decay. 

Breastfeeding is different to bottle-feeding because...

The latch 

Nipples - babies don’t suck the nipple, they have a wide mouth which is filled with boob & nipple. The nipple landing at the junction between the soft & hard palate, resulting in no pooling of milk in the mouth, the milk bypassing the teeth and going straight down the throat. 
Bottles  - these sit much further forward in the mouth (which can lead to a tongue-thrusting habit and a change development of the jaw, teeth and facial muscles) meaning that the milk, can pool in the mouth, near and on the teeth.

The milk 

Breast Milk is so clever, it changes depending on what your baby needs and contains millions of live cells, including;
White blood cells & stem cells.
Lactoferrin, which has antibacterial properties
Antibodies which neutralise bacteria
Formula changes all the time, as companies try to mimic breast milk. It will nourish your baby, but it doesn’t contain all of the live cells, and clever feedback systems our body has evolved over millions of years.

Delivery Device 
Nipples - by month 8 of pregnancy, good bacteria (Bifidobacterium) are secreted from the milk ducts, they then die (they can’t survive outside the body as they are anaerobic) and leave behind potent acids and antibiotic chemicals that repel bacteria. This is thought to prevent naturally occurring bacteria on our skin colonising your babies mouth! 
Bottles - grow a biofilm, that is filled with bacteria, as do dummies/pacifiers, this can change the bacteria that colonise your babies mouth. These bacteria are linked to dental decay. These bacteria can be transferred from parents into the babies mouths. This is why you should never “clean” a dummy in your mouth before putting it in your babies mouth. 

Theories of why breastfeeding sometimes causes decay in some babies 

Bacterial Load - Streptococcus mutans. He’s a little B*&TARD, he is the bacteria that is responsible for decay. He can be passed from parent to baby by kissing, sharing spoons and parents cleaning dummies in their own mouths before popping them in your babies mouth. This is called vertical transmission, i.e from mother to child.

Sugar - Consumption of free sugars in your babies diet from food and drinks, (bloody grandparents right!) increases as they wean. Most foods that are marketed as “healthy” weaning food & drink (stick with water and milk) are jam-packed (no pun intended) with sugar. It’s very misleading for parents, you can easily not know your baby is eating high levels of sugar.

Fluoride exposure - Baby teeth not being cleaned with fluoride toothpaste as soon as they erupt.

Delivery Device - If you put breastmilk in a bottle, the latch changes, meaning the milk doesn’t naturally bypass the teeth.
Enamel Defects - It is very rare, but if the teeth have not formed correctly, they will be at greater risk of dental decay. 

But for now remember, most children (I have only ever met 3 in my entire 10-year career as a dentist for whom this is the exception) will NOT get decay from on-demand breastfeeding past 12 months, and it is magic for you and your baby. 

 My advice is this

Trust your instincts, you are their parent, do what feels right for you and your child.

Continue on-demand feeding if this feels right for you and your baby, the world health organisation advice is to breastfeed until 2 years and beyond. 

Keep their mouth clean

Use baby dental wipes that contain Xylitol to reduce the bacteria in your babies mouth that can cause decay BEFORE the teeth erupt.

When the first tooth erupts (usually around 6 months) brush it! Brush twice a day with a fluoride toothpaste.

Limit free sugars

Food and drink that humans have messed with (don’t have mud on them still!) generally contain added sugar that 100% does cause decay. So control this variable wherever possible. Don’t add sugar to weaning foods, and try and stick to water and milk.

Get the right support 

Register with a dentist, and have a check-up when they get their first tooth, or when they turn 1, whichever is sooner. 

Take the advice of your professionals, they will keep a close eye on your child's dental development, and they will be able to spot any problems early and advise if any changes need to be made.


Virtanen, Jorma I et al. “Oral health behaviors and bacterial transmission from mother to child: an explorative study.” BMC oral health vol. 15 75. 3 Jul. 2015, doi:10.1186/s12903-015-0051-5

Tham R and others. ‘Breastfeeding and the risk of dental caries: a systematic review and meta‐analysis’ Acta Paediatrica 2015: volume 104(S467), pages 62 to 84


Special thanks to several people in helping me write this blog. They have contributed to the content, and fact checking and I couldn’t have done it without them. 

Dr Claire Stevens, Mum, Consultant in Paediatric Dentistry, and saver of children's teeth. Dr Laura Lenihan, Mum, instagram boss and family GP, and Charlotte Young, Mum, author, breastfeeding counsellor and lactation consultant. 

I would like to just take this chance to say that I have been tinkering with this blog for well over 8 months. The reason? I am nervous and worried that I will upset people. Please know that I have conflicts in my mind, between Dentist Katie (having to only advise from a strong evidence base) and regular Katie (who is endlessly pragmatic). 

This blog is intended to help parents understand how best to look after their children's teeth, and is in no way ever asking parents to not breastfeed for as long and however, they choose. Likewise, I am being brave, and having a conversation many dental care professionals have been desperate to have for a long time, so they can better support and help their patients. So, with this in mind, if you have feedback I would love to hear it, but please be kind and remember we are all in this together! 

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