How frequently should non-alcoholic mouthwashes be used?

Question

Foreword: I ask this only for mouthwashes with no alcohol; so please omit alcoholic mouthwashes (which may hurt the mouth and may have been claimed to cause cancer).

My grandmother uses the Crest Pro-Health Rinse which contains 'anti-microbial agent, cetylpyridinium chloride'. Yet USA Today in 2008 and CTV News in 2012 reported complaints that the mouthwash browns and stains teeth, and also numbs taste. From the CTV article:

The parent company of Crest, Proctor and Gamble, told CTV News that the ingredient Cetyl Pyridinium Chloride is what causes some people’s teeth to turn brown.

Dentist Shaireen Lalani says the stains are not permanent and can be removed with professional cleaning.

In some cases, Crest has reimbursed consumers to have their teeth professionally cleaned.

What are the risks to using such mouthwashes? Most mouthwashes recommend two rinses daily, but is this advice safe and correct? How often should they really be used?

Answer 1

You don't need at all to use any mouthwash. A healthy mouth is full of bacteria, almost all of them beneficial for our health, and

1. There is no evidence so far of any long term preventive effect of any kind of mouthwash, only trials with transient effects (< one year) or 6 months in surrogate clinical endpoints as number of bacteria and gingivitis. The only one with some evidence are fluoridated-based mouthwashes, but you get the same effect if you don't spit after brushing with fluoridated toothpaste;
2. If you still decide to use, the only risk is the staining and metallic taste from chlorhexidine-based mouthwashes. There is no evidence so far of risk of oral cancer associated with the use of essential oil–containing mouthrinses.

Instead, you may invest your money in cheese for your oral health.

Lastly, if you are interested in joining a study to increase our limited knowledge about mouthrinses for oral health, there are some trials recruiting.

So, in brief: daily use of fluoridated toothpaste without spitting after using it is enough if you already are eating enough fruits and vegetables and limiting the consumption of sugar.