A red tongue can be a sign of certain nutrient deficiency or oral problems such as:
The deficiency of folic acid or vitamin B-12 can make your tongue appear red. Hence you certainly need to increase your vitamin intake by following a nutritious diet practice.
Benign migratory glossitis
It is a harmless and non-contagious condition making map-like patterns on your tongue. This condition can be a significant symptom of various allergies, deficiencies, diabetes or stress.
A bacterial illness making your tongue look red and bumpy. To highlight, scarlet fever if left untreated, can lead to more serious disorders affecting the heart, kidneys, and other organs.
A common disease in infants and kids causes the tongue to appear red, accompanied by other symptoms such as high fever, inflammation of blood vessels etc.