I HAVE (HAD) EMOTIONAL ISSUES seems the cause for me
I don't have any bowel, stomach, leaky gut or any digestive problems but I suffered with SD for about 20 years until I found baking soda was useful to kill yeasts by reading Italian doctor dr. Simoncini
As far as I understand my case is not linked to internal organs, but just yeasts overgrowth.
Don't think yeasts are on the surface of your skin, they are deeply inside living there and simply washing or using shampoos will not kill them never. They hide and come back. My chest was so infected that nothing was useful until baking soda.
What I do believe is that stress can facilitate overgrowth