There's some good evidence that using chlorhexidine can help with mouth ulcers.   
Chlorhexidine (brand names Chlorohex, Corsodyl) is an antiseptic. It's available as a mouthwash, gel, or mouth spray to use every day. It probably works by keeping away germs that could infect your mouth ulcers and make them worse.
If you use chlorhexidine antiseptic, your mouth ulcers may be smaller and less painful, and they may go away faster. But chlorhexidine probably won't affect how often you get mouth ulcers.
We found four good-quality studies ( randomised controlled trials) of antiseptic mouthwashes or gels for recurrent mouth ulcers.    They included a total of 203 people. The studies compared chlorhexidine or similar products with dummy mouthwashes or gels ( placebos). They showed:
People using chlorhexidine had mouth ulcers for fewer days over four to six weeks  
Using chlorhexidine made mouth ulcers less painful  
Mouth ulcers went away more quickly when people used chlorhexidine or a similar product, but in most studies the average difference was less than a day   
One of the studies showed that people got fewer new mouth ulcers when they used chlorhexidine gel. But there were problems with the way this study was done, so we can't rely on it.  The other four studies didn't show this result.  
The disadvantage of chlorhexidine is that it has a bitter taste and may make you feel sick.  If you use it every day, it can stain your teeth and tongue brown.  This discolouration should go away when you stop using it.
Another antiseptic mouthwash is called hexetidine (brand name Oraldene). There hasn't been much high-quality research on hexetidine as a treatment for mouth ulcers. We only found one small study, which included 40 people with recurrent mouth ulcers.  People who used hexetidine did not feel any better than those who were using a placebo (dummy) treatment.
Another antiseptic is called thymol. It's found in Listerine mouthwash. But there hasn't been much high-quality research on thymol for mouth ulcers. One study found it worked no better to reduce the symptoms of mouth ulcers than a dummy treatment (placebo). 
A placebo is a 'pretend' or dummy treatment that contains no active substances. A placebo is often given to half the people taking part in medical research trials, for comparison with the 'real' treatment. It is made to look and taste identical to the drug treatment being tested, so that people in the studies do not know if they are getting the placebo or the 'real' treatment. Researchers often talk about the 'placebo effect'. This is where patients feel better after having a placebo treatment because they expect to feel better. Tests may indicate that they actually are better. In the same way, people can also get side effects after having a placebo treatment. Drug treatments can also have a 'placebo effect'. This is why, to get a true picture of how well a drug works, it is important to compare it against a placebo treatment.
randomised controlled trials
Randomised controlled trials are medical studies designed to test whether a treatment works. Patients are split into groups. One group is given the treatment being tested (for example, an antidepressant drug) while another group (called the comparison or control group) is given an alternative treatment. This could be a different type of drug or a dummy treatment (a placebo). Researchers then compare the effects of the different treatments.
For more terms related to Mouth ulcers
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