By Dr. Marvin Singh, MD
February 18, 2019

Have you all heard of the Gut-Psoriasis Axis? Well, you have now! These days there is so much discussion about the gut microbiome and how it is connected to everything else in our bodies. For those who are not familiar, the gut microbiome refers to the trillions of bacteria, fungi, and viruses that live inside of our gastrointestinal tracts. Believe it or not, these microbes would weigh the same amount as the human brain if you were to lump them all together into a ball. There are ten times more microbes inside of our gut than we have human cells making up our bodies! Even more amazing is the fact that the DNA from all these little bugs outnumber our human DNA by a factor of 100 to 1! So, yeah, the gut microbiome is definitely a formidable force.

There have been a lot of links between the gut microbiome and chronic diseases, namely inflammatory and autoimmune diseases. One of the ways the gut microbiome is connected to the rest of the body is felt to be through a circuitry of various other different microbiomes. Yes, there is a skin microbiome too! Some feel that there is possibly cross-talk between the various microbiomes and that could influence the bacteria on our skin and our immune system. Changes in the skin microbiome have been demonstrated to promote inflammation of the skin and perhaps this has to do with communication and interaction between the skin and gut microbiomes.

A recent systematic review was conducted by scientists at UCSF and Georgetown University. They found that the skin microbiome showed a trend towards having more Streptococcus and lower amounts of Propionibacterium in those with psoriasis. In the gut microbiome, the ratio of Firmicutes and Bacteroidetes was disturbed in psoriasis and Actinobacteria was not as prominent as might be expected. The authors felt that while these sorts of correlations are relatively new discoveries, there seem to be associations with psoriasis and changes in microbiome composition and this could potentially be a place where specific treatments can be focused on.

Psoriasis is a chronic inflammatory systemic disease so it only makes sense that the gut microbiome may play a role in it since at least 70% of our immune system is located in the gut and the gut microbiome plays a large role in influencing systemic inflammation. It is felt that imbalances in the gut microbiome can lead to vulnerabilities in the barrier of the gut and this could be a key factor in the development of conditions like psoriasis. A small study published in the Journal of Dermatology in December 2018 demonstrated that dysfunction of the intestinal barrier (aka intestinal permeability or leaky gut) in psoriasis disrupted the natural balance between the microbes in the gut and the immune system.

Another nice article written recently suggested that the gut microbiome influences skin balance and health by its influences on systemic immunity. Certain bacteria and products produced by those bacteria (metabolites) like retinoic acid and polysaccharide A from Bacteroides fragilis, Faecalibacterium prausnitzii can promote the accumulation of certain kinds of white blood cells called regulatory T cells; and, this helps facilitate anti-inflammatory responses. On the other hand, there are certain bacteria, like segmented filamentous bacteria, that promote inflammation by calling into action certain kinds of white blood cells like Th17 and Th1 cells. What I found fascinating from reviewing this article is that the DNA of intestinal bacteria have been isolated from the blood of those with psoriasis. So, hang on for a minute and think about that. This further supports the theory that a disrupted intestinal barrier might allow intestinal bacteria (and their metabolites) to get into the bloodstream and then build up in the skin and disrupt the balance of the environment in the skin. Furthermore, short chain fatty acids, like butyrate, that are produced by beneficial bacteria in the gut, are felt to play a key role in influencing what kinds of bacteria live on the skin, which in turn can impact the skin’s immune defense mechanisms.

This is all such a fascinating and ever growing field in medicine. I tell people that when Hippocrates, the father of modern medicine, said many years ago that “all disease begins in the gut” he probably didn’t have a clue what he was talking about but he was spot on! More and more we are building a growing body of evidence that supports links between the gut microbiome and a myriad of different diseases and conditions. This is even more reason to focus on gut health in everything that we do!