Leaky Skin Syndrome

Dear Colleagues,

The gut and skin are the largest organs in humans, both of ectodermic embryonic origin and acting as a barrier to protect the body from environmental pollutants, allergens, toxins and pathogens. The intestinal barrier prevents the loss of water and electrolytes and the entry of antigens and microorganisms into the body from crossing into the blood with tight intercellular junctions, allowing for only specific nutrients to pass. The deep part of the gut barrier is populated by a network of immune and nervous cells organized in two specialized structures called “gut associated lymphoid tissue” (GALT) and the “enteric nervous system”, respectively. It is named the “second brain” due to the number of constitutive neurons and its relationship with the central nervous system. In healthy conditions, the intestinal barrier forms a tight barrier that controls what is absorbed into the bloodstream.

An unhealthy gut lining may have intercellular cracks, allowing external material from the lumen to penetrate the blood and travel to the brain, lungs, and skin. This syndrome is named leaky gut, also known as increased intestinal permeability, and is a digestive condition in which bacteria (pathogenic and opportunistic strains), viruses, and toxins are able to “leak” through the intestinal wall. This leaking triggers i) inflammation (named a cytokine storm), which could be massive, and ii) sub-clinical changes in the gut flora that could lead to problems within the digestive tract and beyond.

The main origin for leaky gut syndrome is dysbiosis, characterized in the gut by a decrease in microbial diversity with the expansion of specific bacteria, which can trigger bloating, depression, IBS, and eventually even cancer. The composition of the gut microbiota is dynamic and influenced by a number of regulators: the microbiota itself through diversity and end balance, diet, the quality of intestinal mucosa, mucus, stress, and the immune system. The gut microbiota plays a critical role in digestion, the production of hormones and vitamins, inhibiting the growth of pathogens, and assisting with drug and toxin metabolism. A number of diseases, including inflammatory bowel diseases as well as metabolic disorders such as obesity and diabetes type II, are associated with intestinal dysbiosis.

The skin is the largest organ in humans, and one of its most important functions is acting as a barrier to protect the body from environmental fluctuations including pathogenic infection. The protective barrier function of the skin is implemented by the epidermis and host innate functions associated with commensal microbiota living on the tissue. The skin barrier function is known to be affected not only by external environmental factors, such as temperature, humidity, ultraviolet (UV) rays, and chemicals, but also by a variety of other factors, including psychological stress and the physiological conditions of the body, such as nutritional status.

Although the majority of microorganisms that live on the human skin are harmless and even beneficial, some resident microorganisms are potentially pathogenic under certain conditions. For example, Staphylococcus aureus, a common cause of skin and systemic infections, resides in the skin of 10–20% of healthy individuals as a harmless commensal, but can also colonize the lesioned skin of ∼90% of atopic dermatitis (AD) cases and other dermatoses like psoriasis and acne vulgaris.

As described in the gut, in healthy conditions, the skin forms a tight barrier that controls external stimuli including microorganisms, and leaky epithelial syndrome might be a link between unhealthy microbiota, which explains many disorders including digestive infectious diseases and dermatitis. One of the most important functions of the skin is to protect the host from harmful environmental stimuli including invasion by pathogenic strains. Like in the gut, an unhealthy skin characterized by a dysbiosis lining may have intercellular cracks in the stratum corneum and deeper layers, allowing external material to penetrate the skin, blood as well as the brain, lungs, and gut.

A leaky epithelium is the new source of inspiration for explaining and fighting chronic and infectious diseases. In this Special Issue, we aim to focus on research in this field, which could provide a new application of microbiome unbalance. For example, to maintain and improve healthy skin conditions, a wide variety of skin-care ingredients are on the market, but none of them try to specifically repair the intracellular cracks induced by dysbiosis and pathogens and opportunistic bacteria in tight junctions.

Dr. Lionel Breton
Guest Editor

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