Your gut lining is what protects you from the outside world, deciding what makes it in and what is kept out. The cells that make up the gut lining are joined together by what are called tight junctions.
These junctions slacken to let nutrients from your food in and tighten to keep toxins or pathogens out. When tight junctions are irritated they can separate, causing too big a gap in the gut lining.
Think of overstretched cheesecloth. When your gut lining is compromised in any way, an increasing number of foods may irritate your gut and beyond, and that irritation may even show up on your skin. One key to gut health is having a strong and toned gut lining.