Allergic reactions are pretty common.
Tomatoes contain a compound called histamine, which boosts the immune system to fight against foreign invaders. That usually comes in the form of allergic reactions like rashes and swelling of the tongue, among other unpleasant effects. For those already diagnosed as being allergic to tomatoes, those symptoms can be even more severe.
They might give you acid reflux.
Tomatoes are very acidic and can cause heartburn in people with stomach problems like gastritis and gastroesophageal reflux disease. Even if you’re healthy and eat too many tomatoes or too much tomato sauce, you might end up with that familiar burning sensation.