Fundamentals
How teeth whitening works
Teeth are not white on the inside. Under the enamel sits a layer called dentin, and dentin is naturally yellow. Enamel itself is closer to transparent than to white, so the shade you see is mostly dentin showing through. That leaves two ways to lighten a tooth: scrub stain off the outside, or use peroxide to bleach the color inside. Nearly every whitening toothpaste does the first one.
Your tooth color comes from underneath
Light passes into the enamel, reflects off the dentin below, and comes back out. The dentin sets the basic color. The enamel decides how much of it you see.
Thicker, more opaque enamel hides more dentin. Thinner enamel shows more. This is why a person with genuinely healthy teeth can have a yellower smile than the person next to them.
Much of this was settled before your teeth came in
Enamel is built once, before a tooth erupts, and your body never rebuilds it. How thick it ended up, and how yellow the dentin under it is, are largely set by development and by genes. One common variant in a gene called ENAM has been linked to thinner enamel in adults, and inherited conditions like amelogenesis imperfecta can leave enamel discolored or fragile.
Then age moves things in one direction. Your tooth keeps adding new dentin on the inside while enamel wears and thins on the outside, so more yellow shows through over the years. Teeth darken with age even with excellent brushing.
No toothpaste makes enamel thicker or dentin less yellow. Your starting shade is a real constraint, not a hygiene failure.
Two kinds of discoloration, only one removable
Within minutes of cleaning your teeth, saliva lays a thin protein film over them. Colored compounds in coffee, tea, red wine and tobacco bind to that film. Some mouthwashes and iron supplements stain it too. This is extrinsic stain, and it genuinely comes off.
Other discoloration sits inside the tooth. Tetracycline antibiotics taken while teeth were forming, dental fluorosis, a knock that killed the nerve, and inherited enamel or dentin disorders all color a tooth from within. No brush reaches that.
Two mechanisms wear the same word
Stain removal. Small hard particles polish stained film off the surface. Other ingredients, such as pyrophosphates and hexametaphosphate, loosen the stain or stop it settling again. This lightens a tooth by taking something off it.
Oxidation, which is actual bleaching. Hydrogen peroxide is a small molecule that diffuses through enamel into dentin. There it forms reactive oxygen species that break apart the colored molecules inside the tooth. This changes the tooth's own color.
Only the second is bleaching. Both are sold under one word, and that is where most of the confusion in this category starts.
What toothpaste can honestly do
Whitening toothpaste really does remove more surface stain than regular toothpaste. Two separate meta-analyses of controlled trials found that effect consistently. If your teeth look dull from coffee and tea, that is a real benefit.
What it does not reliably do is bleach. One of those reviews found that pastes with added whitening chemicals performed about as well as those without, which points at the abrasive doing most of the work. In a trial against a 10% carbamide peroxide gel, a whitening toothpaste did no better than plain toothpaste, and both were far behind the gel.
Contact time explains much of the gap. Toothpaste sits on your teeth for about two minutes before you spit it out. A bleaching tray sits against them for hours.
What whitening costs
The abrasives that lift stain can also wear tooth structure. Healthy enamel handles normal brushing well. The risk rises on exposed roots, on teeth softened by acid, and when people brush harder hoping for a faster result. Our article on abrasivity covers that in detail.
Peroxide has its own trade-off. Sensitivity and gum irritation are the common side effects. They are usually mild and temporary, and they get more likely at higher concentrations. The American Dental Association notes sensitivity can affect up to two-thirds of users.
The claims that do not hold up
In the United States, "whitening" is not a regulated term with a defined test behind it. A paste that scrubs off coffee stain can carry the same word as a gel that bleaches dentin. In 2014 the Food and Drug Administration said most peroxide tooth whiteners meet the definition of a cosmetic rather than a drug.
Europe drew the line differently. A product sold straight to consumers there is capped at 0.1% hydrogen peroxide, and anything from 0.1% up to 6% has to come through a dentist. That gap is worth remembering when a US label promises dramatic results.
Three claims deserve suspicion. Charcoal: a review in the journal of the American Dental Association found no adequate clinical evidence behind the safety and effectiveness claims, while the advertising promised antibacterial, antiviral and detoxifying effects that nothing supported. Blue pigment: some pastes deposit a blue film that makes teeth look less yellow while it sits there, which is a color trick rather than bleaching. "Removes years of stains": a stain-removal claim written in the shape of a bleaching claim.
The short version
- Enamel is nearly transparent. The color you see is mostly the dentin underneath it.
- Enamel thickness and dentin shade are largely set by development and genes, and no toothpaste changes either.
- Teeth darken with age because dentin thickens inward while enamel thins outward.
- Surface stain from coffee, tea, wine and tobacco comes off. Stain inside the tooth does not.
- Abrasives remove stain. Only peroxide changes a tooth's own color.
- Whitening toothpaste reliably reduces surface stain. It does not reliably bleach.
- In the US "whitening" is a marketing word, not a standard. Charcoal and blue pigment carry the weakest evidence in the category.
Read the full evidence review The optics of tooth color, the chemistry of peroxide, what the whitening-toothpaste meta-analyses actually measured, and why US label claims outrun them.
One word covers two chemically unrelated interventions. One takes material off the outside of a tooth. The other diffuses into it and oxidizes the molecules that absorb visible light. They differ in mechanism, in the discoloration they can address, in effect size and in risk. Almost every misleading claim in this category comes from letting a single label carry both.
Key points
- Tooth color is mostly dentin chroma read through translucent enamel. Enamel is roughly 96% mineral by weight and near-colorless; dentin is roughly 70% mineral with about 20% organic material, and that organic fraction carries most of the color.
- Enamel is formed once and is not remodeled. Enamel thickness, dentin shade and developmental defects are set before eruption, which places a genuine ceiling on what any surface treatment can achieve.
- Peroxide bleaching works by diffusion and oxidation. It is the only common consumer mechanism that changes the intrinsic color of tooth tissue rather than removing something deposited on it.
- Whitening dentifrices reduce extrinsic stain relative to regular dentifrices in meta-analysis. The same analysis found no clear advantage for formulas carrying added chemical whitening agents, which locates the effect in the abrasive system.
- The 2018 Cochrane review of home bleaching found effects over placebo across 71 trials but rated the certainty of that evidence low to very low, and could not conclude which agent, concentration or regimen is superior.
- In the United States most peroxide whiteners are regulated as cosmetics and "whitening" has no defined test behind it. In the EU, consumer sale is capped at 0.1% hydrogen peroxide.
Where tooth color actually comes from
A tooth is a layered optical system, not a painted surface. Incident light is partly reflected at the enamel surface, partly scattered within the enamel, and partly transmitted to the dentin, where it is absorbed and scattered before returning. Perceived color is the integral of all of that. Enamel contributes gloss, translucency and opalescence; dentin contributes most of the chroma.12
The composition explains why. Enamel is approximately 96% mineral by weight with only 1% to 2% organic matrix. Dentin is approximately 70% mineral, 20% organic and 10% water. Chromophores are organic molecules, so the tissue with twenty times more organic material is the tissue that carries the color.3
This is the single most useful fact in the subject. A treatment confined to the enamel surface is working on the layer that contributes the least color. Anything that changes the tooth's own shade has to reach dentin, or has to change how much dentin the enamel lets you see.
- Enamel
- ~96% mineral
- Dentin
- ~70% mineral, ~20% organic
- Color source
- Mostly dentin
Color is quantified in the CIE L*a*b* system, where L* is lightness, a* runs green to red and b* runs blue to yellow. Most tooth whitening, by any mechanism, shows up as a rise in L* and a fall in b*. Holding onto that coordinate system matters later, because at least one commercial technology moves b* without touching the tooth's actual pigment.1
What differs between people, and what is fixed at formation
Enamel is unique among mineralized tissues in that it is produced once, by ameloblasts that die at eruption. Bone remodels and dentin can be added throughout life. Enamel cannot be rebuilt biologically. Whatever thickness and structure a tooth erupted with is the thickness and structure it keeps, minus wear.
That formation is under genetic control. A non-synonymous polymorphism in the enamelin gene ENAM, T648I (rs7671281), has been associated with thinner enamel in living humans.4 At the pathological end, amelogenesis imperfecta is a group of inherited enamel defects with reported prevalence between roughly 1 in 700 and 1 in 14,000 depending on the population studied. Affected enamel can be hypoplastic, hypomineralized or both, and teeth may be discolored, sensitive or prone to disintegration.5
A caution about how far this can be pushed. It is well established that enamel formation is genetically controlled and that specific variants and disorders alter enamel thickness and appearance. It does not follow that normal variation in tooth color between healthy people has a clean, quantified heritability. That specific number is not well established, and any product or article that assigns a percentage to it is going beyond the evidence.
The defensible version of the genetic claim is narrower and still useful: baseline tooth color is substantially determined by tissue characteristics laid down before eruption, and those characteristics are not modifiable by anything applied to the tooth surface afterwards. Two people with identical hygiene can have visibly different natural shades.
The lifetime trend runs one way
Two independent processes darken teeth with age. Secondary dentin is deposited on the pulpal surface continuously through life, thickening the highly chromatic layer. Meanwhile enamel is progressively lost to attrition, abrasion and erosion, thinning the translucent layer in front of it. Both changes increase the dentin contribution to perceived color.
The relationship is consistent enough to have forensic value. A 2025 systematic review and meta-analysis found dental color measurement usable as an age estimation method in adults, which is only possible because the underlying change is systematic rather than idiosyncratic.6
This matters for expectation setting. A 55-year-old and a 20-year-old are not starting from the same substrate, and no dentifrice reverses secondary dentin deposition.
Extrinsic discoloration: a film problem
Within minutes of a professional clean, salivary proteins adsorb onto enamel to form the acquired pellicle. The pellicle is not a defect; it is a functional layer involved in lubrication and in mineral exchange with saliva. It is also the substrate on which extrinsic stain accumulates.7
Chromogens from dietary polyphenols in tea, coffee and red wine bind to pellicle proteins, in some cases through metal ion bridging. Tobacco combustion products deposit and polymerize. Cationic antiseptics, chlorhexidine in particular, produce a characteristic brown stain by a related mechanism, and iron salts produce a black one. Chromogenic bacteria account for some black line staining. Watts and Addy's classification separates these by whether the compound is itself colored or becomes colored after binding.78
Because this material sits on the tooth rather than in it, it is mechanically and chemically removable. This is the entire addressable market for whitening toothpaste, and it is a real one. Pellicle chemistry is also why stain returns: the film re-forms within minutes and the same chromogens are still in the diet. Any stain removal result is a steady state, not a permanent change. Our article on saliva and oral health covers the pellicle's protective functions in more detail.
Intrinsic discoloration: a tissue problem
Intrinsic discoloration is incorporated into enamel or dentin and cannot be removed by anything acting on the surface. It divides usefully by timing.8
Pre-eruptive. Tetracyclines administered during odontogenesis chelate calcium and are incorporated into mineralizing tissue, producing yellow to gray-brown banding that darkens with light exposure; minocycline can discolor already-formed teeth in adults by a separate route. Excess fluoride during enamel formation produces fluorosis, ranging from faint white flecking to brown mottling with surface pitting. Systemic illness, nutritional deficiency and inherited disorders of enamel and dentin formation also fall here.
Post-eruptive. Pulp necrosis after trauma releases hemoglobin breakdown products into dentinal tubules, darkening a single tooth. Internal resorption, some restorative and endodontic materials, and the age-related dentin changes described above all alter color from within.
The clinical distinction that marketing erases. Extrinsic stain and intrinsic discoloration have different causes, different mechanisms and different treatments. A product that is highly effective against the first can be entirely ineffective against the second while advertising a single undifferentiated promise of "whiter teeth."
The mechanisms, separated
A chemist's review of the category sorts consumer whitening agents into six functional classes: abrasives that remove stain mechanically, antiredeposition agents that prevent chromogens depositing, colorants intended to produce a white appearance, proteases that degrade the protein component of pellicle and stain, peroxides that oxidize organic chromophores, and surfactants that lift hydrophobic compounds off the surface.3 Only one of those six changes the color of tooth tissue.
Removal: abrasion, chelation, enzymatic action
The abrasive system is the primary functional ingredient in most whitening toothpaste.13 Hydrated silicas, calcium carbonate, calcium phosphates and alumina remove pellicle-bound stain by mechanical action. Polyphosphates, principally pyrophosphate and sodium hexametaphosphate, adsorb to enamel and both displace existing chromogens and interfere with their redeposition. Enzymes such as papain and bromelain target the protein scaffold of the stained pellicle.
These are real mechanisms with real effects, and they are limited by definition to material that is on the tooth. They also carry the category's main mechanical risk, which our article on toothpaste abrasivity treats in full. Abrasivity and stain removal are correlated but not locked together: a well-engineered abrasive can clean efficiently at low relative dentin abrasivity, which is why sodium bicarbonate lifts stain while sitting at the low end of the scale.
Oxidation: what bleaching means chemically
Hydrogen peroxide has a low molecular weight and no charge, so it diffuses through the interprismatic spaces of enamel and into dentin rather than sitting on the surface. Carbamide peroxide is a delivery form that dissociates to hydrogen peroxide and urea, at roughly a three-to-one ratio, so 10% carbamide peroxide yields approximately 3.5% hydrogen peroxide.910
In the tissue, peroxide dissociates into reactive oxygen species including hydroxyl and perhydroxyl radicals. These attack the conjugated double bond systems that make chromophores absorb visible light. Breaking a long conjugated chain into shorter fragments shifts absorption out of the visible range, so the molecule stops contributing color.910
The mechanism is not perfectly selective for stain. Work published in 2012 found that peroxide whitening correlated with oxidation of the tooth's own organic matrix, not only of deposited pigment, and argued that the loss of organic material is itself part of the whitening effect.11 A later mechanistic review reached a compatible conclusion, describing an affinity-based process affecting sound enamel and dentin alongside stain molecules.9 Bleaching is therefore better understood as oxidation of organic material within the tooth than as targeted stain destruction.
What peroxide bleaching actually achieves
The 2018 Cochrane review is the reference point for home bleaching. It included 71 randomized trials: 26 studies with 1,398 participants comparing a bleaching agent to placebo, and 51 studies with 2,382 participants comparing agents to each other. Carbamide peroxide and hydrogen peroxide in trays, strips, paint-on gels and mouthwashes all whitened teeth relative to placebo over two weeks to six months.12
The certainty attached to that finding was low to very low. Two of the 71 trials were at low overall risk of bias; 67 were unclear. Concentrations, application methods and durations varied so widely, and most comparisons rested on such small single trials, that the review could draw no conclusion about which composition, concentration, application method or treatment duration is superior. Tooth sensitivity and oral irritation were the most common adverse effects, more prevalent at higher concentrations, and generally mild and transient. Whitening had no effect on oral health-related quality of life.12
Read that result precisely. Peroxide bleaching works: it is the one consumer mechanism with a plausible chemical route to intrinsic color change and trial evidence of effect over placebo. What the evidence does not support is any specific claim about one product, concentration or protocol beating another. The category's confidence is not matched by the certainty of its literature.
What whitening toothpaste actually achieves
The strongest evidence for whitening dentifrices is on extrinsic stain, and it is positive. A 2018 systematic review and meta-analysis screened 851 papers and included 21 publications covering 32 comparisons of whitening against regular dentifrice over at least six weeks in adults. Whitening dentifrices reduced natural extrinsic stain across every index used. For stain area on the original Lobene Stain Index the difference of means was −0.44 (95% CI −0.55 to −0.34); for overall stain intensity it was −0.35 (95% CI −0.44 to −0.25).14 An updated 2025 meta-analysis of 14 randomized trials reached the same direction of effect, with substantial heterogeneity between studies (I² = 91%).15
Two qualifications carry most of the weight. The first is what was measured: these are stain indices scored on tooth surfaces, not shade changes in the tooth's own color. The second is the subgroup finding. The 2018 review's authors concluded that the benefit held "irrespective of whether or not a chemical discoloration agent was added." If formulas with added whitening chemistry perform about as well as those without, the abrasive system is doing the work, and the chemistry named on the front of the box is not what is producing the measured result.14
Head-to-head trials against real bleaching make the ceiling explicit. A double-blind randomized trial assigned 75 participants with shade C1 or darker to a conventional toothpaste, a blue covarine whitening toothpaste, or 10% carbamide peroxide for four hours a night. Across every timepoint there was no difference between the whitening and conventional toothpastes on shade or on any CIE L*a*b* parameter. The carbamide peroxide group showed significantly greater color change at two and four weeks, and both toothpaste groups reported more dissatisfaction with their tooth appearance.16
Contact time is the structural reason. A toothpaste is in contact with enamel for roughly two minutes and is then diluted by saliva and expectorated. A tray or strip holds a higher peroxide concentration against the tooth for hours. A chemistry that depends on diffusion into dentin cannot be delivered on a two-minute schedule at consumer-legal concentrations.
Optical agents, charcoal, and the weak end of the category
Blue covarine
Blue covarine is a pigment that deposits on enamel during brushing and stays there. Because blue and yellow are opposed on the b* axis, a thin blue film lowers b* and raises perceived whiteness without altering the tooth's own pigment. The mechanism was published by the manufacturer's own researchers, who described it accurately as an optical approach.17
The effect is real, immediate and superficial, in the literal sense. It is a deposited layer that can be removed and must be reapplied. Independent clinical evidence has not been kind to it: the randomized trial described above found no benefit over conventional toothpaste on any color parameter.16 An in vitro comparison of whitening technologies on tea-stained bovine incisors did find blue covarine and microbead abrasives performing best of the products tested, which illustrates how far laboratory ranking and clinical benefit can diverge in this category.18
Charcoal
A 2017 literature review in the Journal of the American Dental Association searched for clinical trials of charcoal dentifrices with at least three months of follow-up and found none that met inclusion criteria out of 118 articles screened. Of the studies that existed, three reported deleterious outcomes including increased caries and enamel abrasion. The authors also sampled 50 consecutive charcoal dentifrices sold online and cataloged the advertising: unsubstantiated antibacterial, antifungal, antiviral and "oral detoxification" claims were routine, and one third of the products contained bentonite clay. The conclusion was insufficient data to substantiate either the safety or the efficacy claims of the category.19
Charcoal is not established to be dangerous, and that is not the claim here. It is a category sold on specific advertised benefits for which the supporting evidence does not exist, and whose only plausible whitening mechanism is the abrasion any dentifrice provides.
Risk, on both mechanisms
Mechanical. Whitening formulations have measured across a wide abrasivity range, and category words on the label do not predict where a given product sits. The exposure that matters is not a single number but the combination of abrasive system, brushing force, frequency, and the substrate being brushed. Exposed root dentin and acid-softened enamel are the vulnerable cases. That subject is covered in full in our abrasivity article.
A 2022 systematic review pooling in vitro studies found whitening toothpastes increased enamel surface roughness and reduced surface microhardness relative to controls. The meta-analysis rested on four studies and the work is laboratory work, so it establishes a measurable surface effect and a direction of concern rather than a quantified clinical consequence.20
Chemical. Tooth sensitivity and gingival irritation are the well-documented adverse effects of peroxide bleaching. The American Dental Association reports sensitivity affecting up to two thirds of users, typically appearing within two to three days and usually resolving by the fourth day after treatment.23 A 2025 network meta-analysis of 77 randomized trials found sensitivity risk rising with concentration: carbamide peroxide at 20% to 22% and hydrogen peroxide at 14% to 16% carried roughly a threefold higher risk than hydrogen peroxide at 2% to 4%. Average intensity was mild across all agents, and the quality of evidence was rated low.21
An earlier critical review of the biological aspects concluded that bleaching at accepted concentrations, properly supervised, has a favorable safety profile, while noting effects on enamel surface morphology, on restorative materials, and the importance of soft tissue protection.22 The honest summary is that peroxide bleaching is not established to cause clinically significant permanent enamel damage at consumer and professional concentrations, and that unsupervised use of high concentrations is a different proposition from either.
Why the claims on a US shelf are so loose
"Whitening" is not a defined regulatory term in the United States and carries no required test. A dentifrice whose entire effect is polishing away coffee stain may use the same word as a peroxide gel that oxidizes chromophores in dentin, and neither is obliged to say which it is doing.
The classification question was put to the Food and Drug Administration directly. In a 2009 citizen petition, the American Dental Association asked the agency to classify peroxide tooth whiteners as drugs. FDA's April 2014 response concluded that most peroxide-containing tooth whiteners meet the statutory definition of a cosmetic, and that there were insufficient data to determine whether the products as a group meet the definition of a drug.24 Cosmetics do not require premarket approval for safety or efficacy.
The European Union answered the same question differently. Council Directive 2011/84/EU, applied from 31 October 2012, caps hydrogen peroxide at 0.1% in products sold directly to consumers. Products containing more than 0.1% and up to 6% may only be supplied through a dental practitioner, with the first application of each cycle carried out by or under the direct supervision of a dentist, and not for use on anyone under 18. Above 6% they cannot lawfully be placed on the EU market as cosmetic tooth whiteners.25
The two regimes are looking at the same chemistry and reaching different conclusions about who should supervise it. Neither is obviously correct. But the gap is the clearest available explanation for why claims on a US shelf can outrun what is in the tube, and why "as seen in dental offices" does not mean the strength used in one.
One useful signal survives. The ADA Seal of Acceptance is granted to over-the-counter whitening toothpastes and whitening strips whose manufacturers have submitted evidence of safety and efficacy for review. Professional products dispensed or applied by dentists are not eligible for it, so its absence on those means nothing.23 Our article on free-from labeling covers the same structural problem in a different category.
Where the evidence is weak
Measurement is the first problem. Much of the clinical literature scores color against physical shade guides, which are ordinal, unevenly spaced and observer-dependent. Spectrophotometry gives continuous CIE L*a*b* values, but studies mix instruments, illuminants and color difference formulas, which makes effect sizes hard to pool honestly. Stain indices measure a different construct again.
The second problem is who funds the work. Several of the foundational reviews and the original blue covarine papers were authored from within the oral care industry: references 1, 2, 13 and 17 were led from Unilever Oral Care, and reference 3 has two authors from a manufacturer's research department. That does not invalidate the methods or the results, and industry laboratories do much of the competent work in this field. It belongs beside the findings rather than hidden from them.
Third, a large share of the mechanistic and comparative evidence is in vitro, often on bovine incisors artificially stained with tea, brushed by machine. That design isolates product differences well and predicts clinical benefit poorly, as the divergence between the laboratory ranking and the clinical trial of blue covarine shows.1618
Finally, the outcome is cosmetic and self-assessed, which makes expectancy effects unusually strong and blinding unusually hard. It is difficult to blind a participant to whether they are wearing a bleaching tray. This is a genuine reason to weight the placebo-controlled evidence heavily and to treat before-and-after photography, lighting and all, as marketing rather than data.
References
- Joiner A, Luo W. Tooth colour and whiteness: a review. Journal of Dentistry. 2017;67S:S3-S10. PMID 28928097.
- Joiner A, Hopkinson I, Deng Y, Westland S. A review of tooth colour and whiteness. Journal of Dentistry. 2008;36 Suppl 1:S2-S7. PMID 18646363.
- Epple M, Meyer F, Enax J. A critical review of modern concepts for teeth whitening. Dentistry Journal. 2019;7(3):79. PMID 31374877.
- Daubert DM, Kelley JL, Udod YG, et al. Human enamel thickness and ENAM polymorphism. International Journal of Oral Science. 2016;8(2):93-97. PMID 27357321.
- Crawford PJM, Aldred M, Bloch-Zupan A. Amelogenesis imperfecta. Orphanet Journal of Rare Diseases. 2007;2:17. PMID 17408482.
- Martín-Martín J, Santos I, Gaitán-Arroyo MJ, Suarez J, Rubio L, Martín-de-las-Heras S. Dental color measurement to estimate age in adults: a systematic review and meta-analysis. Forensic Science, Medicine and Pathology. 2025;21(1):382-400. PMID 38459359.
- Watts A, Addy M. Tooth discolouration and staining: a review of the literature. British Dental Journal. 2001;190(6):309-316. PMID 11325156.
- Hattab FN, Qudeimat MA, al-Rimawi HS. Dental discoloration: an overview. Journal of Esthetic Dentistry. 1999;11(6):291-310. PMID 10825865.
- Kwon SR, Wertz PW. Review of the mechanism of tooth whitening. Journal of Esthetic and Restorative Dentistry. 2015;27(5):240-257. PMID 25969131.
- Carey CM. Tooth whitening: what we now know. Journal of Evidence-Based Dental Practice. 2014;14 Suppl:70-76. PMID 24929591.
- Eimar H, Siciliano R, Abdallah MN, et al. Hydrogen peroxide whitens teeth by oxidizing the organic structure. Journal of Dentistry. 2012;40 Suppl 2:e25-e33. PMID 22925924.
- Eachempati P, Kumbargere Nagraj S, Kiran Kumar Krishanappa S, Gupta P, Yaylali IE. Home-based chemically-induced whitening (bleaching) of teeth in adults. Cochrane Database of Systematic Reviews. 2018;12(12):CD006202. PMID 30562408.
- Joiner A. Whitening toothpastes: a review of the literature. Journal of Dentistry. 2010;38 Suppl 2:e17-e24. PMID 20562012.
- Soeteman GD, Valkenburg C, Van der Weijden GA, Van Loveren C, Bakker E, Slot DE. Whitening dentifrice and tooth surface discoloration: a systematic review and meta-analysis. International Journal of Dental Hygiene. 2018;16(1):24-35. PMID 28573755.
- Hajisadeghi S, Khansari M, Yazdanian M, Keykha E. Effect of whitening dentifrice on discoloration of tooth surface: an updated systematic review and meta-analysis. BMC Oral Health. 2025;25(1):610. PMID 40254592.
- Meireles SS, de Sousa JP, Lins RBE, Sampaio FC. Efficacy of whitening toothpaste containing blue covarine: a double-blind controlled randomized clinical trial. Journal of Esthetic and Restorative Dentistry. 2021;33(2):341-350. PMID 32820846.
- Joiner A, Philpotts CJ, Alonso C, Ashcroft AT, Sygrove NJ. A novel optical approach to achieving tooth whitening. Journal of Dentistry. 2008;36 Suppl 1:S8-S14. PMID 18646364.
- Vaz VTP, Jubilato DP, Oliveira MRM, et al. Whitening toothpaste containing activated charcoal, blue covarine, hydrogen peroxide or microbeads: which one is the most effective? Journal of Applied Oral Science. 2019;27:e20180051. PMID 30673027.
- Brooks JK, Bashirelahi N, Reynolds MA. Charcoal and charcoal-based dentifrices: a literature review. Journal of the American Dental Association. 2017;148(9):661-670. PMID 28599961.
- Jamwal N, Rao A, Shenoy R, Pai M, Aparna KS, Anupama BR. Effect of whitening toothpaste on surface roughness and microhardness of human teeth: a systematic review and meta-analysis. F1000Research. 2022;11:22. PMID 35265322.
- Terra RMO, Favoreto MW, Morris T, Loguercio AD, Reis A. Effect of at-home bleaching agents and concentrations on tooth sensitivity: a systematic review and network meta-analysis. Journal of Dentistry. 2025;160:105891. PMID 40484311.
- Dahl JE, Pallesen U. Tooth bleaching: a critical review of the biological aspects. Critical Reviews in Oral Biology & Medicine. 2003;14(4):292-304. PMID 12907697.
- American Dental Association. Whitening. ADA Oral Health Topics. ADA Oral Health Topics.
- US Food and Drug Administration. Response to citizen petition from the American Dental Association regarding peroxide-containing tooth whitening products. Docket No. FDA-2009-P-0566. April 2014. Docket FDA-2009-P-0566.
- Council Directive 2011/84/EU of 20 September 2011 amending Directive 76/768/EEC concerning cosmetic products, for the purpose of adapting Annex III thereto to technical progress. Applied from 31 October 2012. CELEX 32011L0084.
This article is educational and describes published research on tooth color, discoloration and whitening. It is not medical or dental advice, not a diagnosis, and not a claim about any product. Athena Naturals does not sell a whitening product and makes no whitening claim. If a tooth has darkened on its own, or you are considering bleaching, ask a dentist first: a single discolored tooth in particular can indicate a problem that whitening would only cover up.
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