Could your toothpaste be behind your mouth ulcers? Three clinical studies suggest yes.

What is SLS, and what does the clinical research say about your mouth?

Sodium Lauryl Sulphate (SLS) is a surfactant, a detergent-type ingredient that creates foam. Its primary function is foaming, not cleaning. It's there because people associate lather with cleanliness. It's cheap, effective at foaming, and has been in mainstream toothpastes for decades.

The problem is what it does to the inside of your mouth.

Your oral mucosa, the soft tissue lining your cheeks, gums, and the floor of your mouth, is protected by a thin layer of mucin proteins. This mucin layer acts as a barrier: it keeps tissue hydrated, shields it from minor abrasion, and maintains the environment that healthy oral bacteria need to thrive.

Research indicates SLS can dissolve that mucin layer. Every time you brush with an SLS-containing toothpaste, you may be reducing the protective coating on your oral tissue. For many people this causes low-grade irritation they never connect to their toothpaste. For those prone to mouth ulcers, known clinically as recurrent aphthous stomatitis, the effect appears significantly more pronounced.

Without the mucin barrier, minor trauma from eating, talking, or accidental biting may trigger the ulceration cycle. The tissue may be less able to protect itself.

What 30 years of clinical research has found about SLS and oral health

The relationship between SLS and oral mucosal health has been the subject of clinical research since the early 1990s. Here's what the published evidence shows:

If you've tried changing your diet, reducing stress, or taking vitamins for your mouth ulcers with no improvement, your toothpaste may be a variable worth testing.

The wider picture: research suggests most toothpastes can disrupt your mouth's entire bacterial ecosystem.

Your mouth is home to over 700 species of bacteria. The vast majority are beneficial, they protect your gum tissue, regulate pH, produce natural antimicrobial compounds, and form the first line of immune defence for your body.

Conventional toothpastes, through SLS, artificial antibacterials like triclosan, and harsh preservatives, may not distinguish between the bacteria you want to remove and the bacteria you need to keep. Research suggests they can affect the wider oral ecosystem, twice a day.

Research associates a disrupted oral microbiome with:

The concern raised by researchers in this field: for some people, the products designed to clean their teeth may be working against the health of their oral tissue, quietly, twice a day.