S.,
This may sound strange but I have to ask... Since it only happens when he eats solid foods and I imagine he is feeding himself, what are you using to wipe down his highchair or table where he is eating from? If you are using any type of wipes, like Clorox or Lysol, the chlorine or pesticides in them are extremely caustic and could be causing the reaction. Even cleaners like 409 or Mr. Clean can be pretty harsh on his little immune system. Try just wiping these surfaces down with plain ole soap and water and rinse thoroughly before letting him eat off of them.
From one mom to another, I never realized how many chemicals were in the products in our home until it started effecting my children.
Good luck and let me know if that helps. If you have any other questions or need suggestions, send me a note.
Have a blessed day,
T. S.