Hello, Possible causes of red (ranging from pink to reddish-purple) tongue is Folic acid and vitamin B12 deficiency. From how long you have these red rash on tongue ? . Accidentally biting your tongue or scalding it on something straight out of the oven can result in a sore tongue until the damage heals. Grinding or clenching the teeth can also irritate the sides of the tongue and cause it to become painful. Smoking excessively can irritate your tongue and make it sore.Quit smoking if its due to trauma don't worry it heals . If its because of other cause you need to consult physician.