“We tried to calm him in every possible way, but he cried and shouted all night“, desperately declared the Coopers about their three-year-old Lukas, who is suffering from severe atopic dermatitis (AD). Stories like this are common in paediatric and dermatologic wards, especially in western developed countries. According to the National Eczema Association, 10% of the world population will develop AD at some point in their life, with prevalence in early childhood (< 4 years old). But although atopic dermatitis cases have significantly increased in the last decade, most current treatments are not effective or come with side effects. Fortunately, there seems to be some light at the end of the tunnel, as pioneering discoveries on the skin microbiome have led to new knowledge and novel treatments being developed. But before we introduce them, let’s talk about the trillions of microorganisms we harbour in our skin and gut.

The term microbiome refers to all the microbial communities (bacteria, fungi, viruses) thriving within and on the human body. These communities live in perfect balance, protecting the human body from the colonization of external and harmful microorganisms. However, when a disbalance happens, a disease might be triggered. In 1920, C. Arthur Scheunert, a German veterinarian, coined the term dysbiosis, referring to a microorganism imbalance on the skin or in the gut. Dysbiosis can be triggered by intrinsic and extrinsic factors. The intrinsic factors are linked to the body’s immune system and hormonal changes, while the extrinsic factors encompass pollution, sun exposure, diet, antibiotics, cosmetics, stress, and the environment.

Today it is known that the skin microbiome and the immune system are deeply connected and communicate with each other. The immune system can change the skin microbiome by modifying the skin’s environmental conditions. Vice versa, the skin microbiome can influence and even control the immune system. Atopic dermatitis is a clear example of how the immune system modulates the skin microbiome. As a confused football player tackling his teammates instead of the opponents in a match, this disease is caused by the mistaken activation of the immune system, leading to the assault of healthy skin tissue.

In many AD patients, the immune system stops producing sufficient filaggrin in the skin. Filaggrin is a protein that provides structure to the lower layers of skin and hydration to the upper layers. As filaggrin becomes scarce, the skin dries, changing the conditions where bacteria live and triggering an imbalance that allows infectious bacteria to take over the skin. Among those is Staphylococcus aureus, aka S. aureus, a bacteria highly resistant to antibiotics and the hallmark of AD. All the current antibiotic treatments for AD aim to kill S. aureus. But before we dig deeper into the causes and possible solutions, let’s follow Lukas’s story.

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It all started when he was nine months old. His mom noticed a swollen rash on his forehead and small raised bumps. She called the paediatrician and was prescribed an ointment. But the ointment did not work. Over the next couple of weeks, the rash extended to his cheeks and scalp and the initial small, raised bumps turned into large patches of red, flaky skin. Some areas had bumps that would ooze pus liquid when barely touched by his clothes or toys. Lukas’s skin became very dry, and he began to scratch himself. The scratching led to more side effects like scarring, darkening, and thickening of the skin. In less than three months, his legs, arms, and stomach developed the same red, itchy, and flaky patches.

Luka’s mom wakes up early every morning and prepares him for daycare. She undresses him carefully to avoid damaging his delicate skin and cleans his body with a creamy cleanser and wipes. She only bathes him at night because too many showers dry his skin. She then applies a corticosteroid cream to all the red patches and bumpy areas to reduce inflammation and stop the wrong activation of the immune system. She lets it dry and adds another layer of moisturizer with ceramides and hyaluronic acid. She finishes by applying sunscreen.

Meanwhile, Lukas’s dad goes downstairs to the kitchen to make breakfast. He knows by heart the cooking rules, no dairy products, gluten, eggs, soy, wheat, peanuts, rice, or fish. Lukas has several allergies, including pets, dust, and pollen.

Finally, after all the preparatory rituals, Lukas and his parents leave home and head to the daycare. At the doorstep, one of the educators welcomes the family with a big smile. She asks some questions, was he sleeping better tonight? How is he doing with this new treatment? Were you able to rest? Lukas’s parents give short but precise answers. “No, he was restless. His skin must be feeling very itchy. The doctor said we would see a fast improvement, but so far, his discomfort only goes away for a couple of hours. Please take care of him, and do not let him play outside in the dirty soil with the other kids. He might get worse.”

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This last comment, which might seem logical at first glance, worsens the problem. There is now plenty of evidence to assume that the encounters faced by young children’s skin microbiome may have long-term implications on their immune response and microbiome interactions in the future. Recent studies have shown that the microbial composition of the soil is very similar to that of the skin, and that the immune system is moulded during the very first years of life.

A study done in Finland in 2020 shows how environmental changes could influence the skin microbiome and strengthen the immune system. Researchers at the University of Helsinki noticed that the number of children suffering from skin disease in suburban and rural areas was lower than in urban ones. To check if there was a difference, the study focused on seven urban and three nature-oriented daycare centres. They refurbished four urban centre yards with forest floors and turfs for children to play with. After twenty-eight days, the researchers took blood, gut, and skin samples from the different daycare centres to compare the kids’ skin microbiome and immune system. The study showed that kids in nature-oriented daycare centres had more diverse bacteria in their skin and gut than in regular urban daycares. But most importantly, the immune system of children in refurbished urban centres was strengthened, meaning it can be easily fortified just by allowing kids to play with more soil.

Equally important to soil encounters is the diet. As we have already seen in Lukas’s story, children suffering from atopic dermatitis are at a higher risk of suffering from food and environmental allergies. A new treatment to avoid these involves the early introduction, before twelve months of age, of top allergic foods, such as eggs and peanuts, under the supervision of physicians. Another good practice is to nourish kids with healthy whole foods containing fibres, pro-, pre-, and post-biotics. Probiotics are live bacteria and yeast known for having health benefits in the gut and skin. Prebiotics are food ingredients that nourish the probiotics and the beneficial microorganisms already living in our bodies. Postbiotics are all the beneficial molecules produced by probiotics. Probiotics and postbiotics can be found in fermented foods such as yoghurt, kefir, kombucha, kimchi, sourdough, etc. Some examples of prebiotics are green leafy veggies, fruits, garlic, whole wheat, and oats.

Considering skincare products, the right pH and ingredients are the key. The bacteria on the skin prefer an acidic pH to live happily and in balance. Products with a pH between five and three are highly advisable for any skin type, especially for AD. Some of the best ingredients to treat the disease try to enhance the skin barrier and compensate for the lack of filaggrin. Among those ingredients are amino acids, ceramides, niacinamide, hyaluronic acid, and the new exosomes. Doctors might prescribe stronger drugs such as corticosteroids, calcineurin inhibitors, or cAMP inhibitors, to reduce inflammation and suppress the mistaken activation of the immune system. But these drugs can come with side effects such as microbiome imbalances and a decline in skin barrier function.

The design of milder and highly specific medical treatments to remove target bacteria and not harm the rest of the microbial population is currently under research. Preferably, the products could be applied directly on the skin to re-balance the microbiome. Other options involve immune treatments to regulate the skin’s environmental conditions from within and reinforce microbial skin diversity.

The study of the link between the skin microbiome and the immune system is still in its early stages. We known is that they have complex, dynamic two-way communication and that both can significantly influence each other but numerous gaps in these communication pathways must be understood to better tackle and decrease the incidence of atopic dermatitis. Meanwhile, the story of Lukas shows how many things can be done to improve the condition. Parents can stop frowning at their children for playing with soil. Children with AD, specially but not exclusively, should be nourished with healthy whole foods containing fibres and pro-, pre-, and post-biotics. And when considering skincare products, the right pH and ingredients are key.

The bottom line? Remember to never stop playing outside in nature and nourish your body. Your microbiome and immune system will thank you.

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