You mention that a saliva gel has improved your EC by 80%. Interesting, but what is a saliva gel?
I think you have an interesting theory on Xerostomia, and I think there is merit to it. All-in-all, however, I think it may be only a contributing factor to EC and not a root cause.
Wall of text incoming, I just put on my tinfoil hat on this. I apologize for the use of jargon here and there, but it makes the text more concise and better defined in my opinion.
I agree that a dry oral mucosa is a plausible trigger for EC-like symptoms. People of advanced age frequently have extremely dry/ chapped lips due to a dry oral mucosa.
However, I think we all know that saliva itself is not helpful to cure EC. On the contrary. Saliva contains enzymes that actively work to degrade the epidermis. Also, the pH of saliva is poorly matched with that of the (acidic) epidermis, which causes fatty acids in the epidermis to dissolve into saliva. The pH of many other liquids, including water, is also poorly matched with the epidermal pH. This is why the application of water on the lips will only make things worse: due to fatty acids dissolving. These fatty acids are crucial for a functional epidermal water barrier.
Because of this, it’s hard to directly link EC to a lack of oral saliva. Indirectly, however, as you explained there may be a link because a dry mouth may indicate an insufficient antimicrobial defense and thus unchecked growth of Candida. Maybe there is also a link with persistent irritation of the oral mucosa?
I strongly doubt that a dry mouth causes _my_ EC, because I have focused on preventing a dry mouth for at least a year by drinking enough (the same year I used Aquaphor).
Coming back to a unifying theory of the causes of EC in us -- highly diverse EC sufferers.
-Inflammation & infection. Causes (5?):
1. caused by contact allergy (allergic/ hypersensitive to a specific substance)
2. constant biting of the lips causing easy infiltration by external/oral micro-organisms. I think that long-term use of isotretinoin (Accutane) can also promote this easy infiltration by chronically causing extremely dry skin. Highly advanced age can have the same effect (dry skin).
3. (theory) Subtle systemic inflammation (my case? Leaky intestines causing food particles in my blood stream, which triggers inflammation?)
4. (theory) Local inflammation of a different cause than 1 and 2, maybe due to irritation of adjacent tissue? (oral mucosa in Sjoren’s patients?)
5. Compromised immune system (whole body)/ compromised defense against infiltrating micro-organisms (AIDS-patients)
1. (theory) Excessive and persistent blood vessel dilation/ excessive number of blood vessels in the lips, due to years of local inflammation and a high oxygen demand of the tissue (constant and very fast production of skin cells). The effect is excessive oxygenation in the upper layers of skin, preventing the formation of a functional water barrier. Vessels do not disappear after inflammation subsides because there are constant triggers (1. insufficient water maintenance in the skin, 2. high metabolic demand of basal keratinocytes in the lips due to skin cell overproduction).
So, in my case I am wondering if I have inflammatory cause #3 or the post-inflammatory cause. A biopsy of my lips >6 years ago confirmed an absence of inflammation in my lips. However, this may have been just a non-inflammatory episode?
Combinations of all of the above are, of course, also possible. Add on top of that a variety of how well our immune systems work due to eating healthy/ unhealthy, sufficient physical exercise or not, a lot of sun or not (strong sunlight on our lips locally suppresses the immune system), chronic mental stress or not, etc.
End of wall of text.
Let me know what you think, and please correct me wherever I'm wrong!