The only time that eating tomatoes can cause hives is if the person is allergic to them. In some cases when a person has a tomato allergy and ingests some of this vegetable, they can experience a number of symptoms, including hives. Although the allergic reaction is usually not that severe, it can become quite serious for others, causing breathing problems due to the tightening of the airways.
The severity of tomato/food allergies vary greatly from person to person, though usually the symptoms are fairly mild. If you have eaten tomato only to find raised red bumps appearing on your skin, it might be a good idea to limit your consumption of this vegetable or eliminate it entirely.