Some potential causes of a red rash on the tongue include inflammation, mouth ulcers, vitamin deficiency, geographic tongue, Kawasaki syndrome and scarlet fever, according to WebMD and the National Institutes of Health. Red rashes on the tongue may also present with other symptoms such as swelling, pain and bumps, according to Healthline.
Deficiencies of either vitamin B-12 or folic acid are common reasons for the red tongue appearance, according to WebMD. Inflammation from biting the tongue can make it red and painful. A red rash on the tongue might also be due to a condition known as geographic tongue. This condition involves reddish spots that appear on the tongue, most commonly around the outer edges. The condition rarely causes problems and disappears on its own. However, doctors ask that patients who have had the spots for more than 2 weeks or have additional symptoms come into the hospital for a visit.
Scarlet fever can also lead to a red tongue and requires immediate treatment. Patients with scarlet fever will also have a high fever. A less common cause of a red tongue is Kawasaki syndrome, notes WebMD. This syndrome typically involves a red tongue with a slight pink tint. Most patients with Kawasaki syndrome are less than 5 years old and have dangerously high fevers. They can also have swelling in their appendages and need to be treated for the condition immediately.