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Why some toothpastes can cause mouth ulcers

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If you're prone to mouth ulcers, the very product you use for oral hygiene could be partly to blame.

QUESTIONMy husband and I suffered from mouth ulcers for years until we switched toothpaste to one without sodium lauryl sulfate. This was after we read an article that linked ulcers with the chemical. Is there a scientific basis for this? 

ANSWER: In short, yes. Sodium lauryl sulfate is a common toothpaste ingredient that a new scientific review has confirmed may give some people painful mouth ulcers.

Recurrent aphthous stomatitis (RAS), the medical name for the ulcers, affects about one in five people in their lifetime. The round, shallow ulcers take five to eight days to heal. They can make toothbrushing and eating uncomfortable.

They have a variety of triggers. As noted earlier, it's thought there is a genetic predisposition to them, and that stress, menstruation, immune dysregulation and deficiencies of the micronutrients iron, folic acid and vitamin B12 may make people more susceptible. Now, it's been found that toothpastes containing sodium lauryl sulfate (SLS), an anionic detergent, may be aggravating matters.

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SLS, a cleaning and foaming agent, has an antimicrobial effect. It is a well-known skin irritant at high concentrations and, with repeated application, contact dermatitis can occur. There’s also evidence that it is an irritant at the low concentrations found in toothpaste.

SLS reduces the protective barrier function of the top layer of tissue lining our mouth. It may also cause proteins in our tissue to denature, which could worsen ulcers that have already exposed underlying tissue layers inside the mouth.

It has been added to toothpastes for more than 20 years, and questions about it have been around for a similar time.

In 1994, for example, Norwegian researchers did a small clinical trial to see what effect SLS had on 10 patients with multiple minor ulcers. In the three months before the study, the participants had on average 17.8 ulcers. They then used a toothpaste containing 1.2% SLS for three months, followed by an SLS-free toothpaste for the same period.

While using the SLS toothpaste, they had 14.3 ulcers on average. When using the SLS-free variety, they had just 5.1 ulcers, suggesting the detergent was indeed contributing to the problem.

Since then, more clinical trials have been done. Although some have supported the hypothesis that SLS is a cause of ulcers, others have found no difference in the number of ulcer days, total pain scores and number of ulcers between SLS-free and SLS-containing toothpaste.

In May, however, a systematic review was published in the Journal of Oral Pathology and Medicine. It included a handful of double-blind, randomised controlled trials that compared the effects of toothpastes with and without SLS. The combined data showed that SLS-free toothpastes reduced the number and duration of ulcers and ulcer pain.

So, the researchers say, people with recurrent mouth ulcers may benefit from using an SLS-free toothpaste, as you have found.

This article was first published in the July 20, 2019 issue of the New Zealand Listener.