I'm not a doctor, but I suffer from canker sores when I travel or I'm under stress. There have been times when I'm on the road and my entire gum will fill with canker sores to the point at which they connect and make a one inch giant sore.

I feel your pain.

I suffered like this for years and then I started taking lysine and it solved the probably 100%!

According MedlinePlus, which is run by the US National Library of Medicine and the National Institutes of Health, canker sores can be caused by a virus, a weak immune system (i.e. flu), hormonal changes, mechanical irritation (biting your gum), stress (ding! ding! ding!), or low levels of vitamin B12 or folate.

MedlinePlus recommends the following for canker sores:

-- Rinse with salt water (this works well--I've done it many times)
-- Apply a thin paste of baking soda and water (I haven't done this)
-- Mix 1 part hydrogen peroxide with 1 part water and apply this mixture to the lesions using a cotton swab (haven't done this).
-- For more severe cases, treatments include fluocinonide gel (Lidex) or chlorhexidine gluconate (Periden) mouthwash. (I haven't done this).

I've found that Biotene Mouthwash helps, as does using my Waterpic with Listerine in it.
http://www.amazon.com/Biotene-Mouthwash-16-Ounces/dp/B00016QSYU

Lysine pills work best of all for me. I buy the Twinlab brand.

http://www.amazon.com/TwinLab-L-Lysine-500-Capsules-Pack/dp/B001G7QG9K/

http://www.nlm.nih.gov/medlineplus/ency/article/003059.htm
http://en.wikipedia.org/wiki/Lysine

I've had them ever since I was a kid, and I've tried most everything to no avail. Then, while living in France, I tried Eludril Mouthwash (http://www.netdoctor.co.uk/medicines/100000914.html) and it was remarkable. Some things I tried in the past numbed the pain, but this is the only thing that made them go away. I don't know if there's an equivalent in the US, but I grab a bunch of bottles every time I'm in Europe.

The best way to deal with cankers is to not get them or at least reduce the number.
Years ago I read in a magazine that drinking directly from cans could cause canker sores. It isn't the metal but, the handling of the can on the way to the store that is the problem. They are shipped in the open, walked on, and stacked with dirty items on top part of the can where people put their lips to drink.
I stopped drinking from cans (rarely did anyway for taste reasons) and made my husband and father (addicted to Pepsi) also stop. Hubby and Dad used to get lots of cankers. Now almost never. They just take it for granted but, used to suffer with them.
-gadgetenvy

Short answer: Watermelon Frost is the only thing that has ever shortened the healing process for my canker sores from 7-14 days to 1-3 days.

Came over to read this thread after seeing a note on Jason's twitter stream.

I have suffered from canker sores since I was a kid and I've tried tons of remedies, and most in this thread (though never tried Lysine, sounds like a preventative?). They all seem to fall into two categories:

1. Helpful pain relief for a time until the sore goes away
   
2. Not really helpful
   

I recently found one more:

3. cures the sore more quickly than doing nothing or numbing the pain

So I'll cut to the chase: Watermelon Frost rocks!
http://www.healthymagnets.com/images/watermelonfrost.JPG

I was resigned to pretty much doing pain management on my occasional canker sores (stress and mouth cuts as primary causes) until a co-worker suggested I try this Chinese remedy. Willing to give it a try but not seeing much of anything on the internet to give me any hope for it, she gave me a bottle of the stuff. It looks like a mold (dark green powder) and kind of tastes a little like one too though it is supposed to have some sort of breath freshening qualities too (probably because some have menthol). The main ingredient in Watermelon Frost is supposedly compounded from watermelon rind and mirabilite.

I apply the powder directly on to the sore (I don't bother to dry it very much beforehand) and pat it into a thick paste and try to leave it as long as possible before saliva rinses it off. I did this 2-3 times a day. I was blown away with the results as my sore cleared up in 2 days, stopped hurting after 1 and never got large. I thought it was a fluke but the next one did the same. It is faster acting when I catch them when still small. but it works even on larger ones.

Now I keep an extra bottle of the stuff to give away. And I always have one with me when I travel. I found an online source for the one that looks like what my co-worker gave me, which is the same as the pic above. I have seen other brands but not tried any others.

I would love to see some studies on this because it's the only remedy that has ever offered me faster healing of canker sores.

Before Watermelon Frost, for pain management I found that Zilactin-B (20% benzocain I think) worked the best as an oral bandage that lasted the longest (sometimes through an entire meal). If applied to a sore after drying it, Zilactin-B covers the sore with a film that lasts awhile and kept acidic foods from causing additional pain.

http://www.dentist.net/images/zilactin-b-gel.jpg

I still carry Zilactin-B or Orajel Film Forming Gel (similar to Zilactin-B but never lasted as long for me) as something of a security blanket. But I haven't used them much since I started carrying Watermelon Frost.

http://www.orajel.com/images/products/7136_ultra_mouth.jpg

The preservative alum works like a charm EVERY time. Dampen a Q-tip, dip it in the alum, then apply to the canker. Make sure you cover the entire canker (may take two Q-tip dips). It burns for a minute and will make your mouth feel parched. But, like Buckley's, it works! Relieves the pain and clears up the canker quickly.

Rinse with water after a few minutes. Repeat once or twice a day, as needed. I've never had to use it more than twice.

Alum can be found in the spice section of any grocery store. For example:

http://i.ehow.com/images/GlobalPhoto/Articles/4714667/Alum_Full.jpg

My parents have had the same tin can of this stuff (not the one pictured above though) since I was a kid, 44 years, and it still works.

...Dale

I get canker sores when I have bitten my cheek or something similar. The best remedy for me has always been to put powdered Alum on on the sour directly. This is the same stuff used to make pickles. It will pickle the sore to allow it to close up and heal. I won't lie though, it can be painful at first when you put it on, but it works wonders.

Usually the pain lessens in a few days, and they usually heal without treatment in a weak or two. If the sores are large, persistent, or painful, you should see a doctor who would prescribe medication. You should avoid foods that irritate your mouth including acidic or spicy foods. Gum chewing can also cause irritation so this needs to be avoided. You should also brush with a soft brush after meals and floss daily. For pain relief, you can try taking ibuprofen (Advil) or acetaminophen (Tylenol). Other medicines, such as Anbesol, Orajel, Orabase and Zilactin-B, might keep your canker sores from becoming irritated by eating, drinking or brushing your teeth. These medicines are applied directly on the sore. You can also mix equal amounts of Milk of Magnesia and Benadryl Allergy liquid. After it's mixed, you can swish a teaspoonful in your mouth for about 1 minute and then spit it out. If you do this every 4 to 6 hours, your canker sores may hurt less. Some people think that sucking on zinc lozenges, taking vitamin C or vitamin B complex, using a sage-and-chamomile mouthwash or taking a lysine supplement helps their canker sores heal faster. This site has additional information
http://www.medicinenet.com/canker_sores/article.htm

What would be great is a picture of a canker sore so one can determine what exactly we're talking about here. I think a lot of people associate cold sores with canker sores. I know that cold sores are caused by the herpes virus, but what is the medical name for canker sores and what causes them.