Sodium lauryl sulfate (SLS) is in most commercial toothpastes. It's a detergent — the thing that makes toothpaste foam. It also disrupts the protective mucin layer that lines your oral mucosa, and one of the cleaner studies in aphthous ulcer research shows this matters.
The Herlofson & Barkvoll Study (1994)
Herlofson and Barkvoll ran a double-blind crossover trial (PMID: 8088761) with 10 patients who had known recurrent aphthous stomatitis. Participants used SLS-containing toothpaste for three months, then crossed over to SLS-free toothpaste for three months.
Results: Mean ulcer frequency dropped from 14.3 ulcers to 5.1 ulcers per 3-month period when using SLS-free toothpaste — a ~64% reduction. The study was small (N=10) but the crossover design controls for individual variation.
Why the Mechanism Makes Sense
SLS denatures mucin proteins in saliva. Mucins form a protective gel layer over the oral epithelium — the unstirred water layer that physically shields mucosal cells from mechanical and chemical trauma.
Without this layer:
- Minor oral trauma (biting, food contact) reaches mucosal cells more directly
- Immune-activating antigens penetrate the epithelium more easily
- The threshold for triggering the aphthous ulcer immune cascade drops
This isn't speculation — SLS's mucolytic properties are well-characterized in pharmaceutical literature. The toothpaste application just puts SLS into prolonged contact with the oral mucosa twice daily.
What to Switch To
Biotène, Sensodyne Pronamel, and Tom's of Maine SLS-free are the most available options. The active ingredient to avoid is "sodium lauryl sulfate" or "sodium laureth sulfate" in the ingredient list.
Biotène
Biotène Fresh Mint Toothpaste
SLS-free — clinically relevant for aphthous ulcer sufferers. Also contains enzymes for dry mouth.
View on Amazon →Affiliate link — we may earn a commission
The Limitation
This is one study with 10 patients from 1994. The evidence is moderate, not strong. Several attempts to replicate it have shown positive trends without reaching statistical significance in larger populations — likely because individual variation in SLS sensitivity is high.
The practical argument for switching is compelling anyway: the intervention costs nothing additional (SLS-free toothpaste is not more expensive), the risk is zero, and for the subset of sufferers where SLS is a trigger, the benefit is large.
If you're a chronic sufferer who hasn't tried this, it should be the first thing you change.