Updated 03 April 2018

Why you have horrendously bad breath after eating cheese – and how to fix it

Not even mouthwash can fight this sour stench.

Milk breath. Cheese mouth. The sour stench of worst-date nightmares. What the heck is this foul demon odour and how does one exorcise it?

Millions of bacteria

Firstly, you have to understand your enemy. You probably don’t think about your mouth this way, but it’s technically part of your digestive tract. Chewing is only the first step of digestion.

Read more: Why you have bad breath and how to get rid of it

“Imagine millions of bacteria feasting on particles of food and tissue in our mouth, some giving off smelly waste,” says Dr David Krol, former chair of the American Academy of Paediatrics' section on Oral Health.

As those microbes work to digest milk solids (lactose, proteins, and lipids), they sometimes create excess hydrogen sulphide.

An article in the Journal of Human Physiology confirms this and states that "the most common bacteria to produce these compounds are gram–negative anaerobic bacteria". It the presence of this bacteria that can cause a foul smell. 

Gram-negative bacteria

This is why, post-cheese, your mouth smells like a mound of rotten eggs.

So, what can you do about it?

While you can’t eliminate the smell completely, you can control the aroma by targeting what Dr Krol refers to as the biggest culprits: gram-negative bacteria.

Read more: Sealed with a bacterial kiss

This family of bacteria (which also includes E. coli and chlamydia, by the way) takes shelter below your gum line, between your gums and teeth, and between the grooves of your tongue.

Brush with fluoridated toothpaste

Unfortunately for those who like to swish and spit, mouthwash doesn’t help the gram-negative bacteria situation – and can actually make it worse.

Mouthwash kills all bacteria (not just the stinky kind), which may lead to even worse breath.

Read more: Your mouthwash could protect you from gonorrhoea

To get rid of the gram-negative bacteria, Dr Krol says to brush with a fluoridated toothpaste at least twice a day and, if you have particularly nasty exhalations, after every meal.

Make sure you’re brushing in the places the bacteria live and pick up an inexpensive tongue scraper too. Flossing also helps.

Basically, good oral hygiene can help fight milk breath. The best news? You don’t have to give up eating cheese.

This article was originally published on

Image credit: iStock 




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