Mouth ulcers are easy to spot. They usually appear as sores on your lips, gums, tongue, inner cheeks or roof of the mouth. While red around the edges, mouth ulcers are typically white, yellow or gray in the center. You may only develop one ulcer, or there might be more. Other symptoms could include: Swelling around the ulcer. Increased soreness when brushing your teeth. Pain that worsens when eating spicy, salty or sour foods.