A lot I've read has to do with lowering histamine levels. It really has helped. Every day I take the recommended combination of Zyrtec and Pepcid AC. I actually take this twice a day. There's an important connection between using these, they are H1 and H2 receptors.
Look up jim.bmj.com. Journalism of Investigative Medicine, UK. It is one of many articles online discussing this. Also, you can look up low histamine diets and see what is very high in histamine and avoid these foods. I do not follow this by the book but the foods I try to avoid are: Bananas, tomatoes, spinach, avocados, shellfish, yogurt, aged cheese, pickles, vinegar, sardines, tuna.
The foods that I focus on eating are fish, eggs, brown rice, fruits (NOT citrus) and green leafy vegetables. I know it's very restrictive. Like I said, I don't follow it strictly but started off with just focusing on foods I needed to AVOID. I simply don't buy them. Hope this helps you!