Is it dangerous to kiss someone who’s eaten gluten if you have coeliac disease?

Coeliac disease is not a food allergy or intolerance. It’s an autoimmune disease that makes the body attack the small intestine if gluten (a protein found in wheat, rye and barley) reaches the gut. Even a small amount – a tiny bread crumb – can cause damage and inflammation.

The only treatment is a gluten-free diet. This means completely eliminating foods containing the protein, such as pasta, bread, noodles and many processed products, and preparing food carefully to avoid cross-contamination.

But what about other forms of cross-contamination? One study surveyed 538 adults with coeliac disease about their dating habits and found 39% were hesitant to kiss their partners because of the disease.

But can gluten really be transferred this way, with a kiss? Research is only just beginning to look at this question – here’s what we know.

How harmful is gluten for people with coeliac disease?

Coeliac disease is common: surveys representative of the population estimate it affects one in 70 Australians. However, it tends to be under-diagnosed. Research suggests only 20% of those with coeliac disease have a medical diagnosis.

This means most sufferers are unaware they have coeliac disease, despite experiencing unpleasant symptoms.

When untreated, coeliac disease can stop the small intestine absorbing nutrients and lead to gut symptoms such as diarrhoea, abdominal pain, bloating and flatulence. It can also result in non-gut symptoms such as fatigue, skin rashes and brain fog.

However, touching gluten won’t have any effect. Gluten only causes damage to people with coeliac disease if it enters the gut. This is why it can be effectively treated with a strict gluten-free diet.

How much gluten is harmful?

Researchers have investigated how much gluten can result in harm to people with coeliac disease. One study found some people with coeliac disease experienced damage to their small intestine with as little as 10 milligrams of gluten per day.

For context, one slice of bread contains 2.5 grams of gluten. A very small amount can cause damage if eaten, such a tiny crumb accidentally transferred from a chopping board or plate.

Australian researchers have determined that a dose of gluten below 3mg does not cause an immune response on very sensitive blood tests.

Food regulatory authorities look at how much gluten is concentrated in particular foods to decide what is “gluten free”. In most countries a diet containing gluten at less than 20 parts per million (or 20mg per kilogram) is considered to be safe for people with coeliac disease.

But Australia and New Zealand have much stricter requirements for labelling a food as “gluten free”. Testing methods in Australia allow for detection as low as three parts per million – this is known as the “limit of detection”. Foods below this limit contain no detectable gluten and can be labelled gluten free.

So, what about kissing?

What does this mean for kissing? Can enough gluten be transmitted from one person to another via saliva to cause problems? To date, there is very limited data.

New US research presented today looked at ten couples, each with one partner who had coeliac disease.

In the study, the non-coeliac partner ate ten crackers containing gluten before the couple kissed for ten seconds.

The researchers found gluten transfer was minimal in the saliva. When the non-coeliac partner had a glass of water after eating the crackers, the gluten in their saliva was less than 20 parts per million (the international limit for gluten-free products).

While this data has not yet been peer-reviewed, their preliminary finding seems to support similar research from 2022 which looked at peanut allergy and saliva to estimate gluten levels in saliva.

It estimated that saliva after eating gluten could contain around 250 micrograms of gluten – one-twelfth of the minimum amount (3mg) believed to cause an immune response.

This means, for people with coeliac disease, kissing should not be an issue to worry about.

Other risks

The bigger risk for people with coeliac disease continues to be exposure to gluten from food – even food labelled “gluten free”.

One study found seven out of 256 manufactured food products sold as gluten free had detectable levels of gluten, in some cases as much as 3mg in a single serving.

In 2018 another study found almost 10% of food sold as gluten free at cafes and restaurants across Melbourne actually contained gluten. One food sample contained a gluten concentration of more than 80 parts per million.

Still, given Australia has strictest regulations in the world, the risk of getting sick from eating gluten-free foods is quite low.

The risk from kissing? Even lower.

If you want to look out for your loved one with coeliac disease, how you prepare food is more important. This includes preventing cross-contamination by storing and preparing gluten-free foods well away from foods containing gluten, and thoroughly cleaning equipment and utensils after they’ve been in contact with food containing gluten.

And next time you’re on a date at your favourite eatery – whether they advertise as gluten free, or just have gluten-free items on the menu – it’s a good idea to politely ask about their food handling practices.