I really do wonder if at least some EC cases are a reaction to an allergen? That was obviously the case for me (SLS was my lip allergen).
We use and come in contact with such a huge range of products, chemicals, etc. It seems possible that people with EC are having allergic reactions to something. And it need not even be the same thing for all people, since an allergic reaction is an allergic reaction regrdless of what one is allergic to.
I used to get a lot of small rash patches on my face and body. They were not a huge problem, mostly an annoyance, but I always found them puzzling. There were several different types, they did not all look the same. I consulted several doctors and dermatologists, and the standard reply was always to give me a steroid cream or ointment of some kind. I have at least ten different ones. To be fair, it usually would clear up the rash, but it would always come back, either in the same spot or a different one. So the steroid crems and ointments were clearly not solving the underlying problem, they just relieved it temporarily.
In an attempt to try and solve the problem, a couple years ago, I switched to all natural skin care, and eliminated all soap, shampoo, lotion, cosmetics, etc that contained any chemicals. All the rashes stopped, and never came back. So it seems to me that the rashes were a reaction to some chemical or other substance I was using?
Bottom line, it might be worth eliminating chemicals from your life to see if it helps or cures your EC.