The digestive system is a place where our bodies come into the most direct contact with the outside world. It’s an extremely active environment and a huge amount of microbes pass through it every single day.
The Digestive System as Part of Immunity
Surely, adequate functioning of the digestive system is an essential component of our health. But just how important is the digestive system and the intestinal microbiota (microbial environment) to our health?
Let’s quickly review some of the main points discussed in earlier in this book:
- The intestinal microbiota appears to have a direct influence on an individuals susceptibility to a variety of chronic diseases 
- A disbalanced gut microbiota may play a role in seemingly unrelated health issues, such as autoimmune disease, diabetes, Chron’s, dermatitis herpetiformis, and atopic dermatitis 
- Germ free animals have been shown to be significantly more susceptible to infection [3, 4, 5]
It really does appear that intestinal issues may correlate with a misbalanced immune system and result in a myriad of health issues and disease. Accordingly, perhaps improving our digestive system and rebalancing our intestinal environments may be of significant value in regaining control of our immune systems.
Making specific connections remains difficult
It seems that a common issues researchers face is making any direct connections (especially for diseases that are outside the gut) between certain disease and gut microbiota. However, research in this area continues and perhaps significant advances will be made in the near future.
Gut Permeability and Skin Disease
A critical component the digestive system is the intestinal barrier. This important barrier ensure that the only nutrients are allowed to pass through the various digestive organs, while toxins and foreign substances are kept out.
As noted in the digestion chapter, if the intestinal barrier is not functioning as it should, various issues can quickly arise. These issues begin with foreign materials and pathogens passing into the bloodstream, leading to increased inflammation and general immune system instability.
In todays health magazines and publications, it seems that many individuals believe that intestinal barrier instability is directly related to skin disease. However, the research in this area is much more vague and there haven’t been any clear relationships established. For review, here are some highlights of several small scale studies in this area:
- An investigation of 109 participants with various skin conditions concluded that passive permeability of the small intestine was normal in these individuals 
- Two studies comparing healthy children with those affected by atopic eczema (18 healthy vs 15 atopic and 29 health vs 26 atopic), showed increased intestinal permeability in the atopic group [7, 8]
- Comparison of a total of 18 individuals (10 effected by eczema alone, while the other 8 also had a diagnosed food allergy) showed increased intestinal barrier permeability irrelevant of food allergies 
In the end, there does seem to be some possible connection, but the size of the studies in this area really makes it difficult to draw any valuable conclusions.
Gut Permeability, Stress and Immune Dysregulation
Now what if we shift our focus from finding a direct connection to skin disease and review some potentially relevant topics instead?
For example, the connection between intestinal permeability and depression appears to be much more established [10, 11, 12]. And since there does appear to be connection between skin disease progression and stress, perhaps the role on intestinal permeability in skin disease is more supplementary then it is causative.
A cyclical relationship
This relationship between intestinal permeability and stress appears to work in both directions. Stress can increase intestinal permeability, while at the same time, increased intestinal permeability can lead to increased inflammation and fuel stress.
Whatever the case may be, improving the intestinal barrier can be beneficial for improving general inflammation levels and assist in overall immune system stability . Both of these factors may ultimately reduce seborrheic dermatitis symptoms and help reverse it’s progression.
This section discussed the possible connection between seborrheic dermatitis and digestive system issues. Some of the key points include:
- The digestive system is an integral part of immunity and abnormalities have been linked to a variety of chronic diseases
- Research investigating the link between digestive system issues and skin disease is sparse with only handful of small scale studies on the subject
- Gut permeability has received the most public attention, but evidence linking it to skin disease shows mixed results
- The connection between gut permeability and depression is much more established, so perhaps its role more supplementary
- Improving digestion and the intestinal barrier can help strengthen overall immunity and reduce general inflammation