The common causes of red patches on the tongue are deficiency in B vitamins, geographic tongue, scarlet fever and Kawasaki syndrome, according to WebMD. Canker sores cause shallow ulcers that have a red margin.
Deficiency in vitamin B-12 and folic acid leads to a red tongue, states WebMD. Geographic tongue causes red patches that look like a map. The patches may shift their position on the tongue and are harmless. Scarlet fever causes a red tongue and a high fever. It mostly affects children between 2 and 10 years of age. Kawasaki disease affects the blood vessels and is common among children under 5 years old. It is not contagious.