Eczema: Understanding the link between gut microbiota and this skin condition.

The microbiota refers to the collection of microorganisms (viruses, bacteria, yeasts) that live in a specific environment. In the human body, there are several types of microbiota (oral, skin, vaginal...), but the intestinal microbiota is the most populated among them.

There are 10 times more bacteria in the gut than cells making up the human body, and 100 times more bacterial genes in the gut than genes in the human genome.

The gut microbiota is a vast ecosystem that is established from birth. Among individuals, there is a tremendous variety in the gut microbiota. However, various factors can influence the composition of an individual's gut microbiota.

• The type of birth.

  The way a child is born conditions a part of their microbiota. For instance, a child born vaginally will have a gut microbiota very similar to the mother's vaginal microbiota, predominantly consisting of bacteria of the type Lactobacillus and Prevotella, whereas a child born via caesarean section will have a gut microbiota similar to the mother's skin microbiota, this time with bacteria of the type Streptococcus, Corynebacterium and Propionibacterium.

• The intake of antibiotics.

  Antibiotics are molecules capable of destroying or inhibiting the growth of microorganisms. Therefore, the intake of antibiotics by the mother during pregnancy or by the newborn at birth can influence the composition of the child's intestinal microbiota.

• Newborn nutrition.

  There is a link between an infant's diet and their gut microbiota. Babies who are breastfed will have fewer Gammaproteobacteria type bacteria than babies who are fed with formula milk, but they will have more of the Bifidobacteria type bacteria.

The gut microbiota plays a crucial role in human health. A rich and diverse microbiota promotes better health. Furthermore, an imbalance in the gut microbiota (dysbiosis) has been highlighted in numerous pathologies. But is there a link with the development of eczema?

According to a scientific study, the gut microbiota of individuals with eczema is composed of specific bacteria that are not found in healthy individuals. Furthermore, an inflammation in the gut microbiota has been observed in some cases. It is therefore suggested that disruption of the gut microbiota in newborns may be the cause of an increased risk of allergies, and therefore of more severe atopic eczema.

Studies have examined the link between the type of milk given to infants (breast milk or formula) and the risk of developing eczema. However, the results obtained vary from one study to another and do not demonstrate that a cause-and-effect relationship exists.

It has also been suggested that the symptoms of eczema could be improved by altering the composition of gut bacteria or by reducing inflammation in the gut. Probiotics, which are living microorganisms like the Lactobacillus found in unpasteurised milk and yoghurt, could facilitate this. A study has indeed shown that administering milk containing prebiotics to children can modulate the gut microbiota.

It would therefore appear that a link exists between eczema and gut microbiota. However, as eczema is a complex condition involving various factors, this link is not currently fully understood.

• REDDY D. & al. Role of the normal gut microbiota. World Journal of Gastroenterology (2015).

• KROLL J. S. & al. Intestinal Microbiota in infants at high-risk for allergy: Effects of prebiotics and role in eczema development. Journal of Allergy and Clinical Immunology (2017).

• VIRTA M. & al. Maternal gut and breast milk microbiota affect infant gut antibiotic resistome and mobile genetic elements. Nature Communications (2018).

• CHAN J. & al. Effects of gut microbiome and environment on the development of eczema in Chinese infants Medicine (2020).