⚠ If you get mouth ulcers regularly, this research is worth 2 minutes of your time
Could your toothpaste be behind your mouth ulcers? Three clinical studies suggest yes.
Most mainstream toothpastes contain a foaming chemical called SLS — and three decades of clinical research have linked it to a thinning of the mouth's protective mucosal lining, a change associated with increased ulceration and slower healing.
Written by the Gutology Science Team · Updated June 2026 · 2 min read
Hero image — SLS foam on tissue / conventional vs. Gutology split / animated mucin diagram
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.
8 in 10
mainstream toothpastes are estimated to contain SLS — including many marketed as "natural" or "sensitive." Check your current toothpaste label.
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.
"Research suggests that every time you brush with an SLS-containing toothpaste, you may be reducing the very lining that helps protect your mouth."
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:
"Patients using SLS-free toothpaste experienced 51% fewer mouth ulcer episodes."
Herlofson BB & Barkvoll P — Acta Odontologica Scandinavica, 1994
A crossover trial comparing SLS-containing and SLS-free toothpastes in patients with recurrent aphthous ulcers. The reduction in episode frequency was statistically significant — and one of the most replicated findings in oral mucosal research.
SLS significantly increased desquamation of the oral epithelium — the shedding of protective mucosal cells.
Herlofson BB & Barkvoll P — Journal of Clinical Periodontology, 1996
A follow-up study confirming the mechanism. SLS doesn't just irritate tissue — it physically degrades the mucosal surface, explaining why SLS users experience more painful episodes and slower healing.
"Complete avoidance of SLS resulted in meaningful reduction in ulcer frequency and severity across all patients."
Shim YJ et al. — Journal of Oral Pathology & Medicine, 2012
Patients who switched to SLS-free toothpaste not only had fewer ulcers — the ulcers they did develop were less severe and healed faster.
If you've tried changing your diet, reducing stress, or taking vitamins for your mouth ulcers — and it hasn't worked — your toothpaste may be a variable worth testing.
"[DR SEB LOMAS QUOTE — to be supplied. Suggested framing: why he recommends SLS-free toothpaste to patients, the link between conventional toothpaste ingredients and mucosal irritation, and why supporting the oral microbiome matters for whole-body health.]"
Dr Lomas holds a First Class Honours degree in Biochemistry and a BDS (Dentistry). He is Clinical Director at Wonder of Wellness and co-founder of the Biological Dentistry programme at Portman Dental Care. He recommends Gutology toothpaste to his patients. GDC Registration: 289356.
Illustration — oral microbiome ecosystem. Healthy (diverse) vs. disrupted. Infographic style.
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:
→ Increased gum inflammation
→ Persistent bad breath
→ Greater ulceration frequency
→ Slower mucosal healing
→ Reduced enamel protection
→ Downstream systemic inflammation
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.
Certification
KIND TO
BIOME®
Independently tested and certified: Gutology does not disturb the oral microbiome.
Most brands claim to be "natural" or "gentle." We put ours through an independent four-phase laboratory protocol — and have the certificate to prove it.
Gutology Toothpaste has been awarded the KIND TO BIOME® mark — independently certified by Kind to Biome AB (Stockholm) and laboratory partner QACS Ltd. The protocol tested the product's real-world influence on 13 microorganisms commonly found in the oral cavity, including live swabs taken from healthy volunteers.
KIND TO
BIOME®
Independently tested and certified microbiome-friendly
Kind to Biome AB & QACS Ltd. Laboratories
Certificate ID: 2026-26 49 03603
- No SLS. No artificial antibacterials. No ingredients that strip the mucin barrier.
- Contains a clinically supported probiotic strain selected for oral microbiome compatibility.
- Independently tested against 13 microorganisms commonly found in the oral cavity — not just an ingredient review.
- Phase 4 testing used real oral cavity swabs from healthy volunteers — live microbiome, not lab cultures.
- Certified microbiome-friendly: independently verified not to disturb the natural oral ecosystem.
- The only UK toothpaste to hold KIND TO BIOME® oral certification.
KIND TO BIOME® is an independent certification body. Gutology has no commercial relationship beyond the testing programme. The mark is awarded solely on the basis of laboratory results. Certificate ID: 2026-26 49 03603. Signed: Beletsiotis Evangelos, Biologist Ph.D, Head of Molecular Microbiology, QACS Ltd.
★★★★★
"I've suffered with mouth ulcers my whole life. I'd had extensive exploratory tests but nothing ever showed up. I swapped my toothpaste and I've not had a problem with mouth ulcers since."
Rosie I. · Verified purchase · 8 months ago
★★★★★
"Within a week the ulcers were fading fast and all sensitivity while brushing had gone. My mouth feels perfectly clean and fresh after using."
Phoebe P. · Verified purchase · 1 year ago
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"Been using this for 4 months. My mouth feels moist for a while after brushing and I've not had any mouth ulcers since starting. Highly recommended."
Richard D. · Verified purchase · 2 years ago
★★★★★
"I no longer have the problem with mouth ulcers — and knowing the product is a natural alternative to enamel preservation is really great. I'm so pleased to have found your product."
Dorothy L. · Verified purchase · 1 year ago
★★★★★
"This has really helped my mouth ulcers and calmed them down so much. Was concerned I wouldn't get that 'just cleaned' sensation, but my mouth feels perfectly clean and fresh."
Sarah C. · Verified purchase · 1 year ago
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