Although it's not my favorite thing to be in the world, I am a mouth ulcer. My street name is most commonly: canker sore. I've got a fancy name, and that involves painful open sores that will exist in your mouth when the mucous membrane breaks. You might also choose to call me one of these other names: aphthous stomatitis or aphthous ulcer. Now that we have that out of the way...
I will often being with a tingling or burning sensation in your mouth. This 'tingling' or 'burning' will exist in the place where the future mouth ulcer, canker sore, aphthous stomatitis or aphthous ulcer will exist. It won't take me longer than a few days to turn into the state of a red bump or spot inside your mouth, which will then be followed by an open ulcer.
Once at the open ulcer state I will appear as a white or yellow oval with an inflamed red border. Modestly I will be approximately 3 mm wide, however, for quick bragging rights, I can reach up to and beyond 1 cm wide in extreme cases. If I've done my job really well, you will be able to see a white circle or halo around the lesion.
My main body, the ulcer, is often times very painful when agitated. This can also be accompanied by sore swelling of the lymph node. If your unsure of where your lymph nodes are, they exist below your jaw. For this locational reason I can often times be mistaken for a toothache at first. Open your mouth, look inside, I'm not!
Your lucky with me, that normally I will go away without any treatment. The best start is to make sure you have good oral hygiene and avoid spicy/acidic/salty foods and drinks. The best and widely known 'home remedy' for dealing with me is to pour salt directly onto my main ulcer. This works but note - can be painful.