The connection between food allergens and skin reactions is mediated by a shared immune response.1 When a new skin condition emerges, it could suggest the presence of an internal immune or inflammatory response, which may be causing or contributing to the skin condition. Conditions such as atopic dermatitis and unexplained rashes may actually be due to a deeper pathophysiological process related to intestinal permeability. Gut inflammation and microbial imbalances, particularly a reduction in Faecalibacterium prausnitzii, have been shown to play a role in conditions such as atopic dermatitis.2
Intestinal permeability: An overview
Increased intestinal permeability, also known as “leaky gut,” describes compromised gut barrier function or integrity. Normally, the intestinal epithelium forms a tightly regulated barrier to control what can enter the bloodstream, allowing for absorption of nutrients and water while excluding harmful substances. If the gut is “leaky,” the intestinal lining becomes more permeable, allowing larger molecules to pass into the bloodstream, including food particles, microorganisms, allergens, and toxins, such as the bacteria endotoxin lipopolysaccharide (LPS). Entrance of these foreign materials into the bloodstream can trigger immune and inflammatory responses in one or more body systems, including the skin.
Causes of intestinal permeability
Compromised intestinal barrier function can result from a variety of contributing factors. These include genetic predisposition, as seen in conditions such as inflammatory bowel disease (IBD), as well as gut infections (bacterial, parasitic, fungal, etc.), dysbiosis, exposure to dietary and environmental allergens, toxins, chronic use of non-steroidal anti-inflammatory drugs (NSAIDs), and physiological stressors such as endurance training.
Symptoms of leaky gut
Increased intestinal permeability may present as a wide range of systemic and gastrointestinal symptoms. Common presentations include the development of GI symptoms such as food sensitivities or intolerances, abdominal pain, bloating and/or diarrhea, as well as systemic symptoms such as joint pain and postprandial brain fog, and skin symptoms like eczema, itching, erythema, and rashes. Intestinal permeability also often coexists with, and may be caused by, other GI disorders such as small intestinal bacterial overgrowth (SIBO) and IBD.
Diagnostic tools
The “gold standard” test for the diagnosis of intestinal permeability is the Lactulose Mannitol test. The patient ingests both lactulose and mannitol sugars, which are not metabolized by the body, and are then measured in the urine. Lactulose, which is a larger synthetic sugar, can only cross the intestinal barrier if it is compromised, while mannitol can cross a healthy gut barrier. An above-normal ratio of lactulose to mannitol suggests a gut permeability issue. An elevated lactulose mannitol ration has been associated with several GI conditions including irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD).3,4
Zonulins are a family of proteins that modulate the permeability of tight junctions between the cells and the digestive tract wall. A blood or fecal Zonulin test is often used as a biomarker for intestinal permeability, however, the analytical validity of this test has been highly questioned. There is ample evidence indicating that available commercial assays are not testing for zonulin at all and that zonulin testing poorly correlates with lactulose mannitol testing.5
Therapeutic approach
Treatment for leaky gut should be personalized for the patient, as causes and symptoms can vary greatly. In practice, this often begins with determining the underlying cause of intestinal permeability such as SIBO, food allergies or intolerances, or IBD. Addressing the cause of intestinal permeability is the first step in reversing it. Lifestyle changes including stress management techniques, dietary changes, reducing or eliminating alcohol, and fasting may be utilized.
Conclusion
Intestinal permeability plays a key role in systemic inflammatory responses that extend beyond the gut. In the context of skin conditions, particularly in atopic dermatitis, compromised intestinal barrier function allows for antigens and other harmful substances such as LPS, to enter the bloodstream.6 This may exacerbate skin inflammation and disrupt epidermal integrity.
Increased permeability is often associated with chronic gut inflammation, dysbiosis, and elevated inflammatory mediators, creating a cascade that reinforces immune dysregulation. Assessment and support of gut health, including the microbiome and mucosal barrier, may offer therapeutic benefit in individuals presenting with unexplained or treatment-resistant skin conditions.
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