Sodium lauryl sulfate (SLS) is a very common anionic surfactant used in many personal care and cleaning products. Anionic surfactants are negatively charged, water loving (hydrophilic) molecules that reduce the surface tension of water. This causes nice bubbly lathers that makes water more effective in cleaning away oil and dirt.
In toothpastes, SLS is used to create foam, help remove debris, and distribute the paste in the mouth. It's cheap and effective, but lately it's been an ingredient that sparks much debate.
Here, we lay out the possible harms, discuss what the peer-reviewed science shows, and conclude with some practical advice.
How SLS Works
SLS lowers surface tension so toothpaste foams and spreads. Because it's a detergent, it can also disrupt lipid and protein layers on mucosal surfaces, for example, the protective mucin layer that coats the mouth's inner lining. This helps explain some of the clinical effects, such as irritation and inflammation, reported with SLS-containing toothpastes.
What Are Surfactants?
Surfactants have a hydrophilic head that is attracted to water, and hydrophobic tail that is attracted to fats and oils. They cluster around dirt and grime, forming spherical micelles which can be lifted and washed away.
How Surfactants Reduce Grease & Dirt
Potential Harms & What the Evidence Says
1) More Canker Sores
Multiple research groups concluded that SLS-free toothpastes reduce the frequency and duration of canker sores, aka. recurrent aphthous ulcers (RAU), in susceptible people. Crossover trials have found that fewer or less-painful ulcers are observed after using an SLS-free toothpaste versus an SLS-containing one.1,2 Recent review studies have concluded that switching to an SLS-free toothpaste can reduce RAU occurrence in people who get recurrent ulcers.3,4
What this means: If you suffer from recurrent canker sores, the evidence supports trying an SLS-free toothpaste as a relatively simple, low-risk intervention.
2) Oral Lining Irritation & Peeling
Some people who use SLS-containing toothpastes experience peeling of the inner cheek lining (aka. oral mucosa). A study following four patients with this problem found that all of them healed within one week of switching to an SLS-free toothpaste.5 Oral mucosa irritation can happen even at concentrations of SLS lower than that typically used in toothpastes (effects are seen below 0.015% SLS concentration, whereas toothpastes typically contain 0.5–2% SLS concentration).6 The reason SLS causes this damage is that it breaks down the protective coating (aka mucin layer) that lines your mouth, making the tissue underneath more sensitive to irritation. Multiple studies confirm that toothpastes with SLS cause significantly more peeling, burning, and itching than toothpastes without it.7
What this means: People with sensitive oral mucosa or a prior history of irritant reactions may notice soreness, peeling, or redness when brushing with SLS-containing toothpastes. People experience a relief from such symptoms after switching to SLS-free toothpastes.
3) Cytotoxicity (Cell Death)
Studies testing SLS directly on human gum cells found that toothpastes containing SLS killed more cells than toothpastes using other surfactants.8,9 The reason appears to be that SLS increases cellular permeability by causing denaturation of cellular proteins, essentially punching holes in cells until they break down. The researchers also warned that this cell damage could slow down healing of gum disease and mouth sores. That said, these tests were done in a lab without saliva present, which in real life helps protect and rinse the mouth during brushing.6
What this means: SLS can kill cells in an in vitro (i.e. petri dish) lab setting, and we have a clear explanation for why; however, whether this causes serious harm during normal toothbrushing depends heavily on how much SLS is used and for how long.
4) Taste Alteration (Temporary)
We've all experienced how terrible orange juice tastes right after brushing. This is because SLS changes how our taste buds interpret flavors! Things may taste more bitter or less sweet than usual. This is a short-term sensory effect rather than a toxicologic harm, but it influences user experience.10
5) Environmental Considerations
Evidence shows SLS can be toxic to aquatic organisms by decreasing dissolved oxygen in the water, and is subject to biodegradation constraints under various conditions. SLS can also lower soil's hydraulic conductivity, meaning water has a harder time moving through it to reach groundwater. Environmental toxicity assessments suggest SLS should be managed to limit concentrations entering waterways.11 These are environmental harms, and not necessarily direct harms to humans, but they matter for sustainability-minded consumers.
Who Should Avoid SLS?
- People with canker sores (aka. recurrent aphthous ulcers): Randomized trials show a reduction of canker sores when patients switched to SLS-free toothpaste.
- People with known oral mucosal sensitivity (e.g. peeling of the inner mouth lining): SLS-free options are shown to reduce irritation and promote healing.
- Children: Because young children are more prone to ingesting toothpaste compared to adults, and there is limited research on the effects of SLS on gastrointestinal systems, it is wise to be cautious.
- General population: For most people, occasional SLS exposure in toothpaste is unlikely to cause systemic harm; irritation is the main concern. If you're otherwise healthy, you may tolerate SLS fine.
- Environmentally conscious consumers: Consider formulations with more biodegradable surfactants or lower SLS content and brands that disclose their wastewater impact.
Final Thoughts
How do I know a toothpaste contains SLS? Read ingredient lists: SLS is listed as sodium lauryl sulfate.
If you notice new or worsening oral irritation after switching toothpaste, see a dentist or dermatologist. Sometimes other ingredients (flavors, essential oils, etc.) can also cause irritation due to allergic reactions.12
If you prefer a conservative approach (i.e. precautionary principle), choosing an SLS-free toothpaste is an easy, low-cost swap to make to your normal dental routine.
The bottom line: SLS isn't dangerous for everyone, but for those who experience canker sores, oral irritation, or sensitivity, switching to an SLS-free toothpaste is a simple, evidence-backed change that can make a real difference.
References
- Herlofson BB, Barkvoll P. Sodium lauryl sulfate and recurrent aphthous ulcers. Acta Odontol Scand. 1994;52(5):257-9.
- Shim YJ et al. Effect of sodium lauryl sulfate on recurrent aphthous stomatitis: a randomized controlled clinical trial. Oral Dis. 2012;18(7):655-60.
- Alli BY et al. Effect of sodium lauryl sulfate on recurrent aphthous stomatitis: A systematic review. J Oral Pathol Med. 2019;48(5):358-364.
- Cheng LL. Limited Evidence Suggests That Patients With Recurrent Aphthous Stomatitis May Benefit From Using SLS-free Dentifrices. J Evidence Based Dental Practice. 2019;19(4):101349.
- Esteves CV et al. Could sodium lauryl sulfate be an irritant factor in oral mucosal desquamation? Int J Case Rep Images. 2020;11:101184Z01CE2020.
- Sabri H et al. The Yin and Yang of Sodium Lauryl Sulfate Use for Oral and Periodontal Health. J Dent (Shiraz). 2023;24(3):262-276.
- Kasi SR et al. Side effects of sodium lauryl sulfate applied in toothpastes: A scoping review. Am J Dent. 2022;35(2):84-88.
- Birant S et al. Cytotoxic effects of different detergent containing children's toothpastes on human gingival epithelial cells. BMC Oral Health. 2022;22(1):66.
- Pecci-Lloret MP et al. In Vitro Biocompatibility of Several Children's Toothpastes on Human Gingival Fibroblasts. Int J Environ Res Public Health. 2022;19(5):2954.
- DeCristofaro P. Why does orange juice taste so bad after you brush your teeth? Chem Matters. 1995 Apr:14-15.
- Asio JRG et al. Sodium lauryl sulfate and its potential impacts on organisms and the environment. Emerging Contaminants. 2023;9(1):100205.
- More D. Signs of Allergic Reaction to Toothpaste. 2025 Oct 10. Verywell Health.