Chronic illness is often at least partially caused by allergic reactions of one sort or the other. Chronic health issues are almost always multifactorial. In other words, there are usually a variety of causes that conspire to create the health problem that a person might face.
People are different and what works well for one might not work so well for the next. That is why treatment needs to be individualized, not treated via the “cookbook” method.
Some people would have to make serious changes in their diet, be treated for allergies, reduce their stress, quit smoking, support the adrenals, and treat with thyroid hormones in order to conquer their illness.