The pain on the left edge of the tongue may be caused by traumatic blood blisters, lobular papillitis, tongue tumor and other diseases, as follows. 1. Traumatic blood blisters: traumatic blood blisters appear on the left edge of tongue due to consuming too hot food, chewing large pieces of dry and hard food, biting, etc. At first the blisters are bright red, and then they become purple-black, and the pain is obvious after the rupture of the blood blisters. 2. Lobular papillitis: the lobular papilla is located at the back of the lateral edge of the tongue, and the lobular papilla is red and swollen in inflammation, and there may be obvious tingling or discomfort. 3. Tongue tumor: if the pain on the lateral edge of the tongue is accompanied by ulceration, hardness on palpation and prolonged healing, it may be a tongue tumor, which needs histopathological examination to make a clear diagnosis. There may be other reasons for the pain on the left edge of the tongue, so it is recommended to go to the hospital in time, and carry out targeted treatment after clarifying the cause of the disease.