Herbs have all sorts of compounds, many of which are known to interact with the body's immune system.

Loads of studies about tumeric and inflammation, arthritis. Also capsaicin, piperine, etc. The list is extensive.

Remember: Herbs and spices are where medicinal remedies originated.

Deep down, AIP is one of those fad diets that prohibit more things than there's evidence for. It's justified based on some pseudoscientific ideas about certain foods causing autoimmune issues. People might say things about intestinal permeability, but the scientific connection can be a bit sketchy.

From. https://thrivingonpaleo.com/aip-spices-and-herbs/

What spices are NOT allowed on AIP? Allspice Anise Seed Annatto Seed Black Caraway Black Cumin Black Pepper Caraway Cardamom Capsicums Cayenne Celery Seed Chili Pepper Flakes Chili Powder Chinese Five-Spice Chipotle Chili Powder Coriander Seed Cumin Seed Curry Powder (typically contains nightshades) Dill Seed Fennel Seed Fenugreek Seed Garam Masala Juniper Mustard Nutmeg Paprika Pepper (from black, green, pink, or white peppercorns) Poppy Seed Poultry Seasoning Red Pepper Russian Caraway Star Anise Steak Seasoning Sumac Taco Seasonin

The idea is that the disorders may not actually be autoimmune, but reactions to certain foods.

I have heard Paprika and chili powder, along with peppers in general, doing something with opening the tight junctions in the gut from Paul Saladino but I can’t recall the what the specific issue or mechanism was.