Swollen Lips. An allergic reaction to tomatoes happens almost immediately after coming in contact with a tomato. Itching and swelling inside or around your lips is one of the first symptoms to develop. The swelling is temporary and lasts as long as the tomato remains in contact with your lips. Remove or swallow the tomato and rinse your mouth and lips with clean water to help reduce the swelling. If you have oral allergy syndrome, you may also display a similar allergic reaction to other fruits and vegetables.