In earlier post I cited the mouth as a possible source of bad bacteria repopulating the gut. Taking oral probiotic lozenges and Spezzata candy(pure licorice) , especially if you have dry mouth could help.
On CFS Remission facebook page (feel free to Like it!), a reader asked about using essential oils (neem, tulsi) on the skin and whether it would impact the gut microbiome? My answer was yes, because the microbiome on the skin (anywhere) is touched by the hands which are then brought into direct contact with food (sandwiches, apples, buns, candies) — unless, perhaps, you are very formal Swedes (I was in a MacDonald’s in Stockholm and saw some parents and children eating fries and hamburgers with forks and knives….).
So, your response may be “but I shower everyday!! No way!!!” As always, let us look at what PubMed says…
- “Human skin is the first line of defense against pathogens, while simultaneously harboring a diverse milieu of commensals, including bacteria, fungi, and viruses. These symbiotic organisms play essential roles in lipid metabolism, colonization resistance to transient organisms, and education of the immune system (Belkaid and Segre, 2014; Grice, 2015; Scharschmidt and Fischbach, 2013). “
- “Despite regular washing and contact with bacteria-laden objects, our personal milieu of skin microbes remains highly stable over time, reports a metagenomics study published May 5 in Cell. The authors say this knowledge could be applied to better understand a wide range of human skin disorders through the development of prebiotic, probiotic, and microbial transplantation approaches.” 
A recent article found that dandruff may result from over abundance of Staphylococcus and undergrowth of Propionibacterium. People shampoo every day and still have dandruff which appears to confirm that the skin microbes maintain themselves. It also begs the question, do you CFS/FM/IBS sufferers have a higher incidence of dandruff (which has a prevalence of 19% in the general population)?
So fixing the microbiome drags all of the way back to the skin surface! My suggestion to the reader was consider using Neem and Tulsi (and… ) soap as a starting point. These are available on Amazon (search there) as well as Neem and/or Tulsi toothpaste. Rotating to different (true) herbal soaps would also be rational! BEWARE of herbal scented soaps — often they lack the herbs and are made with chemical synthetics.
As always, it may not be needed for some and essential for others.