What causes eczema and why is it so common in Hong Kong?

Atopic dermatitis (the most widespread presentation of eczema) is the third most common skin condition globally. In 2017 it was also the greatest skin-related contributor to years of life lost due to poor health, with studies showing that the impact of having eczema is higher than having malignant skin tumours.

“Being such a visible organ, eczema causes great emotional distress in both kids and adults. Itching at night can interfere with sleep and subsequent fatigue can impact mental health.

Leaky gut is one of the causes of eczema, and also contributes to anxiety and depression,” says IMI naturopathic doctor Ji Woon Min.

Research shows that those with eczema are more likely to experience anxiety and depression. Stress is also a known trigger for skin conditions, which can lead to a vicious cycle of worsening symptoms.

In Hong Kong, eczema is estimated to affect 30% of our kids – who are most vulnerable between the ages of one and five years old. Hong Kong’s average of 30% is higher than the global average. A 2020 analysis of data from 195 countries showed that the burden of eczema was highest among wealthy countries – and according to Global Finance Magazine, Hong Kong ranks as the 15th wealthiest in the world.

Dr Ji Woon finds that testing for the root cause of the condition provides real relief for clients. “They finally have an explanation beyond being told ‘It’s just a skin problem.’ Topical treatments don’t find the root cause and keep clients stuck in a cycle of seeing a symptom and applying a band-aid.”

Eczema, asthma and hayfever make up the atopic triad: a group of conditions often occur together and are caused by your immune system’s response to certain triggers.

My toddler has eczema and a runny nose - are they linked?

In a 2023 study, scientists explored the prevalence of the atopic triad 22,123 children. They found that the chances that a child might have all three conditions in their lifetime was 11 times higher than the expected probability of developing the conditions separately. Once a child has developed one of the conditions in the triad, they’re more likely to develop another in future.

“In my experience, it’s very common to see eczema and hayfever together,” confirms Dr Ji Woon.

In atopic conditions, the immune system is hypersensitive to a range of allergens, causing an overproduction of IgE, an antibody which helps protect your body from illness. IgE is the main driver of allergic reactions and elevated levels are associated with eczema.

“In conventional medical settings, you’re mostly tested for IgE, but in our clinic we also test for IgG - a delayed hypersensitive reaction to certain foods. Sensitivities can also impact the development of eczema, just as much as an allergen can,” explains Ji Woon.

The hygiene hypothesis is a theory that more hygienic living conditions have led to lower exposure to infection, and that as a result our immune systems are unable to identify between harmless molecules (like pollen, or dust) and pathogens.

Does the hygiene hypothesis explain the rise in eczema?

During the 60s, scientists witnessed a rapid increase in atopic conditions (eczema, asthma and allergies like hayfever).

In 1989, Dr Strachan coined the hygiene hypothesis. He noted that larger families had a lower risk of developing conditions like eczema and hayfever. He theorised that unhygienic contact between siblings led to higher rates of microbial exposure and infection, which provided protection against atopic conditions. Various studies since have supported the theory that larger numbers of siblings protect against atopic conditions.

“A hyper sanitised lifestyle limits early childhood exposure to a rich variety of microbes, which starves the body of microbial inputs, leading to dysbiosis and eventually resulting in immune dysregulation and allergies,” says Ji Woon.

In 2023, The Standard reported that the average number of kids per household in Hong Kong was 0.9 per couple, reflecting a bias towards being child free, or raising kids in single child households, which could be impacting the microbes they’re exposed to.

There isn’t enough evidence to suggest that washing your hands less could prevent eczema. In fact, one study showed that households where regular vacuuming takes place reduces the risk of a child developing eczema. Similarly, exposure to ‘grime’ and pollution has been associated with an increased risk of eczema.

The relationship between toxins and eczema

The average air quality in Hong Kong is 16.4µg/m³, which is 3 times the recommended WHO guideline of 5µg/m³. Studies show that children who live near roads with heavy traffic are more likely to develop atopic conditions.

Beyond the air in our neighbourhoods, the toxins in the home also play a role. VOCs (volatile organic compounds) are rife in the home – found in children’s toys, furniture and paint. Kids who are exposed to refurbishments in the home have been found to have higher incidence of eczema. Synthetic pillows, which often contain VOCs and allergens are also linked to increased risk.

"VOCs are also found in soaps, laundry detergent, fabric softener and sunscreen. When eczema is triggered by chemical irritants (like VOCs) it's called contact dermatitis. The good news is that when you take steps to remove the irritant, the skin is able to heal," says Dr Ji Woon.

Living in multi-story buildings of 7 floors or more and high indoor humidity are linked to higher risk, likely because these buildings have higher susceptibility to developing mould. Hong Kong is a hotbed for mould, and eczema is one condition among many which is affected by mould.

“One of the most severe cases of eczema I have seen was triggered by mould,” confirms Dr Ji Woon.

Mould has a knock on effect on the gut, causing an imbalance of good and bad bacteria in the gut – which plays an integral role in skin health.

Your gut and skin are connected: why dysbiosis affects eczema

“The most common cause of eczema that I see in my practice is dysbiosis: imbalance in the gut microbiome. This is driven by an interactive, bidirectional pathway known as the gut-skin axis,” says Dr Ji Woon.

The gut microbiome in early life is associated with the severity, remission and flare ups of eczema. Studies on the impact of the gut microbiome on eczema are varied – some suggest that low gut diversity is linked to the development of eczema, while other link high levels of specific species of bacteria to the condition, namely E. coli, Clostridium sensu stricto, and F prausnitzii.

The F prausnitzii study shows a link between eczema and higher levels of a sub-species of the bacteria which doesn’t produce as many short chain fatty acids. They state that this leads to dysregulation of the intestinal barrier – also known as leaky gut. As a result, undigested food, toxins and other substances leak into the body’s circulation. Studies suggest that irregular immune responses have an inflammatory response to these rogue gut particles, which in turn increases inflammation in the skin, exacerbating eczema.

“Your gut lining and skin serve the same purpose: they are protective walls built to let good things in (nutrients and moisture) while locking out the bad – like toxins and pathogens. When one wall fractures, it often triggers a chain reaction that destabilises the other,” Ji Woon adds.

“The gut-skin axis operates as a two way street. When the skin barrier is compromised and inflamed, it releases its own distress signals into the bloodstream. These signals travel back to the gut, where they alter the gut microbiome and can weaken the intestinal lining.”

To assess the impact of the gut on your skin, Ji Woon uses the GI MAP and zonulin test. Vitamin D testing is also important, she reveals.

“Vitamin D functions as a hormone that directly repairs the skin barrier, calms the immune system and manages the skin microbiome. Clinical research shows that those with eczema are more likely to have vitamin D deficiencies, and that a lack of vitamin D correlates with increased eczema severity. While waiting for test results, we remove any potential allergy triggers like sugar, dairy, gluten, eggs, peanuts and shellfish to minimise flare ups.”

What else causes eczema?

Around 10% of the population have mutations in the gene which codes for an important skin protein called filaggrin which protects the skin barrier by binding keratin.  Those with the mutation have a 3.3 times increased chance of developing eczema.

This protein is theorised to affect the way dry conditions (like air conditioned homes) affect the skin barrier, causing dry skin problems like eczema.

Breastfeeding duration is linked to eczema risk. A 2016 review of 14,499 children showed that the children of mothers who breastfed for 1-6 weeks, and those who breastfed for over 6 months had an increased risk of eczema. It’s suggested this is because breastfeeding for extended periods can result in irregular allergen specific immune responses in the gut.

This research may also be a result of reverse causation. “Often, infants who are genetically predisposed to severe eczema show symptoms early on. Mothers may prolong breastfeeding because the child has eczema, rather than prolonged breastfeeding cause eczema,” says Dr Ji Woon.

“Between 4 and 6 months, your baby’s gut has a critical window in which it needs to meet common food proteins like peanut, egg and dairy, to learn not to attack them. Breast milk can act as a protective immune blanket during this phase, helping the gut safely process new proteins. Breastfeeding is particularly important for babies born via C-section – as this can help bridge the gap to match the microbial profile of vaginally born infants,” she adds.

“The foods you eat during breastfeeding matter – one pattern I see again and again in the clinic is that when Mom removes allergens from her diet – her baby’s eczema, and often constipation clears up.”

Other risk factors revealed by the 2016 meta-analysis included the introduction of solid foods before 4 months of age, the introduction of cow’s milk before 9 months and use of antibiotics during your baby’s first year of life.

Do kids grow out of eczema?

80% of children outgrow eczema by age 8 according to a meta-analysis reviewing data from over 110,000 participants. According to the study, kids who displayed eczema later in childhood, those who had it for 10 years and those who had more severe eczema are more likely to have persistent eczema beyond the age of 8.

“Though it may seem as though kids grow out of eczema, often that vulnerability is still there and has just changed shape – appearing instead as a nose allergy. Or, the condition might lie dormant for some time and then re-emerge when you’re under stress, like after undergoing a surgery, going to college, experiencing job stress or moving countries,” says Ji Woon.

If you or your child is struggling with your skin, our naturopaths can help identify and diagnose skin conditions.

Tests can reveal the contributing factors for eczema – allergies can be identified and eliminated, intolerances can be removed temporarily and later reintroduced with the support of a naturopath. You can find out if low gut diversity, or specific strains might be leading to symptoms. And – if pollution or toxins like mould are causing skin issues.

You don’t have to suffer alone – you can find the answers you and your kids deserve.

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