Over-hybridizing, over-exposing.
What we consider natural is highly unnatural: a Chihuahua is vastly different from the ancient natural canine. Wheat is not the same as the ancestral wild grain from which it came.
We eat the same foods all year round. That is also highly unnatural, and increases the allergenic sensitivity.
Although it is very high in gluten, many who react to wheat can eat spelt: It is an ancient, less altered food to which people have not been constantly exposed.
Finally, Leaky Gut Syndrome is real, and allows protein fragments into the blood stream, where they produce an auto-immune response.
Healing the gut lining is the best first step. That may require temporary removal of foods that irritate and damage the villi.
Natural is unhealthy. Lives used to be short,nasty, and full of pain and privation.
If that is what people want, it is pretty easy to get.
Dying of infection is natural.
Having your teeth gone by 50 is natural. (living that long is unnatural)
Losing most of your children to disease and famine is natural.
Constant worry of war, raids, and ambush is natural.
The U.S. has been one of the most unnatural nations to exist in all of history!