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.

Vincent Ho, Associate Professor and Clinical Academic Gastroenterologist, Western Sydney University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Head hair comes in many colours, shapes and sizes, and hairstyles are often an expression of personal style or cultural identity.

Many different genes determine our hair texture, thickness and colour. But some people’s hair changes around the time of puberty, pregnancy or after chemotherapy.

So, what can cause hair to become curlier, thicker, thinner or grey?

Curly or straight? How hair follicle shape plays a role

Hair is made of keratin, a strong and insoluble protein. Each hair strand grows from its own hair follicle that extends deep into the skin.

Curly hair forms due to asymmetry of both the hair follicle and the keratin in the hair.

Follicles that produce curly hair are asymmetrical and curved and lie at an angle to the surface of the skin. This kinks the hair as it first grows.

The asymmetry of the hair follicle also causes the keratin to bunch up on one side of the hair strand. This pulls parts of the hair strand closer together into a curl, which maintains the curl as the hair continues to grow.

Follicles that are symmetrical, round and perpendicular to the skin surface produce straight hair.

Life changes, hair changes

Our hair undergoes repeated cycles throughout life, with different stages of growth and loss.

Each hair follicle contains stem cells, which multiply and grow into a hair strand.

Head hairs spend most of their time in the growth phase, which can last for several years. This is why head hair can grow so long.

Let’s look at the life of a single hair strand. After the growth phase is a transitional phase of about two weeks, where the hair strand stops growing. This is followed by a resting phase where the hair remains in the follicle for a few months before it naturally falls out.

The hair follicle remains in the skin and the stems cells grow a new hair to repeat the cycle.

Each hair on the scalp is replaced every three to five years.

Hormone changes during and after pregnancy alter the usual hair cycle

Many women notice their hair is thicker during pregnancy.

During pregnancy, high levels of oestrogen, progesterone and prolactin prolong the resting phase of the hair cycle. This means the hair stays in the hair follicle for longer, with less hair loss.

A drop in hormones a few months after delivery causes increased hair loss. This is due to all the hairs that remained in the resting phase during pregnancy falling out in a fairly synchronised way.

Hair can change around puberty, pregnancy or after chemotherapy

This is related to the genetics of hair shape, which is an example of incomplete dominance.

Incomplete dominance is when there is a middle version of a trait. For hair, we have curly hair and straight hair genes. But when someone has one curly hair gene and one straight hair gene, they can have wavy hair.

Hormonal changes that occur around puberty and pregnancy can affect the function of genes. This can cause the curly hair gene of someone with wavy hair to become more active. This can change their hair from wavy to curly.

Researchers have identified that activating specific genes can change hair in pigs from straight to curly.

Chemotherapy has very visible effects on hair. Chemotherapy kills rapidly dividing cells, including hair follicles, which causes hair loss. Chemotherapy can also have genetic effects that influence hair follicle shape. This can cause hair to regrow with a different shape for the first few cycles of hair regrowth.

Hormonal changes as we age also affect our hair

Throughout life, thyroid hormones are essential for production of keratin. Low levels of thyroid hormones can cause dry and brittle hair.

Oestrogen and androgens also regulate hair growth and loss, particularly as we age.

Balding in males is due to higher levels of androgens. In particular, high dihydrotestosterone (sometimes shortened to DHT), which is produced in the body from testosterone, has a role in male pattern baldness.

Some women experience female pattern hair loss. This is caused by a combination of genetic factors plus lower levels of oestrogen and higher androgens after menopause. The hair follicles become smaller and smaller until they no longer produce hairs.

Reduced function of the cells that produce melanin (the pigment that gives our hair colour) is what causes greying.

Theresa Larkin, Associate professor of Medical Sciences, University of Wollongong

This article is republished from The Conversation under a Creative Commons license. Read the original article.