I'm not sure of any statistics on the actual correlation between the two, but I do know it is a commonly talked about concept in much of the natural health world, especially in the recent years. I know for me personally, it is related to a point, because I do have celiac disease, so I have always struggled with gut issues and that's my "weak spot" so to speak. However, I have tried all sorts of dietary changes and eliminations, etc. and none ever seemed to make a difference with my skin. I do have to make sure I adhere to a gluten free diet and eat healthy overall, but as for any specific dietary changes, none have seemed to help me personally.
Some say about 70% of our immune cells reside in the gut, in which case it makes sense there's a correlation, but as with anything else, I think it's highly individual. When I spoke to my TCM (Traditional Chinese Medicine) practitioner about the concept, she did agree it's part of it, but that it's much more complex than that and only focusing on the gut is again focusing on just one part of the body, instead of the entire body as a system.
That said, there are many newer tests (such as GI map stool test, among others) that can be done with a holistic doctor or nutritionist to try to find out if there is a correlation. Of course, naturopaths and all of these tests typically aren't covered by insurance and are quite pricey, so it isn't always easy for everyone to have access. But I'd think that would be the way to go if you wanted to try that avenue. Or you could always start small yourself and if you don't already take one, maybe add a good probiotic to your regimen and see if it makes any difference. Of course, always consult with your doctor or team before adding anything new. You can also type "gut", or anything related into the search bar on this site to see more of other's experiences, but hopefully we have a few more chime in here too. 😀 -Nina (AtopicDermatitis.net Team Member)