Many babies develop a mild, temporary red rash or redness around the mouth when eating acidic fruits like oranges, tomatoes, or sweet lime. This is typically a 'contact rash' caused by the acidity of the food on sensitive skin rather than a true food allergy. If the redness is localized to the mouth area, does not cause the baby discomfort, and fades away shortly after the meal, it is usually harmless. However, if you see swelling, rashes on non-contact areas, or if the baby seems distressed, consult your pediatrician to rule out an allergic reaction.