How long does teeth whitening last? What long-term studies found

Is teeth whitening permanent?

No. The NHS, the UK’s health service, says the effect may last around 3 years if you follow your dentist’s advice; the Canadian Dental Association, in a 2007 position statement reaffirmed in 2013, says up to 2 years, depending on smoking and staining foods and drinks. Neither cites a study.

The trials are more precise, mostly for trays worn at home with a peroxide gel. In one trial of 92 adults, teeth were still lighter than at the start two years after whitening, but more than two-thirds of those seen again reported some color coming back, mildly to moderately; an older, smaller study, of 24 people seen again at two years, found the color came back gradually for most of them rather than all at once.

A 2023 review of 24 studies of home whitening reports that most authors find the color stable over follow-ups of 1 to 2.5 years, with more relapse after severe discoloration such as drug-related staining, and that long-term maintenance is not well established. In the 2018 Cochrane review, 53 of the 54 home-whitening trials that reported funding were company-funded, and it rated the certainty of the evidence low to very low.

References: [1] NHS · [2] CDA · [3] Meireles et al. · [4] Swift et al. · [5] Fioresta et al. · [6] Cochrane

How long do strips, trays and in-office whitening last?

The two strip trials with long follow-up cited here used strips with 5.3% hydrogen peroxide. In one, in which 57 adults used either these strips or placebo strips, most of the change remained at 6 months; in the other, of 30 people split between strips and trays, teeth were still lighter than at the start after 18 months, though less than right after treatment. The first trial was funded by the strips’ maker and written by its employees; the second, according to the Cochrane review, by another oral-care company. In the European Union, products sold directly to consumers are capped at 0.1% hydrogen peroxide, so the strips sold in stores there are much weaker than those tested.

In-office results vary. In one trial of 60 people, half whitened in-office and half at home, neither group showed a significant rebound after two years. In another, of 62 people, color came back by about two shade-guide steps after 4.5 years, though the whitening remained clear. In a third, among the 30 people whitened only in-office, the lightness gained was gone after 4 weeks, the end of follow-up, but teeth stayed less yellow; in the 30 who followed with strips, the lightness held.

Sensitivity, one of the most common side effects of home whitening, is usually mild and temporary; if it lingers, that’s one for a dentist to look at.

References: [1] NHS · [6] Cochrane · [7] Gerlach et al. · [8] Auschill et al. · [9] Règlement (UE) 344/2013 · [10] Tay et al. · [11] Hortkoff et al. · [12] Gómez-Polo et al. · [13] Garcia-Godoy et al. · [19] Oral Health Foundation

How fast does teeth whitening work?

Not in a day at home, in the trial the American Dental Association (ADA) cites: in 2005, among 39 people, over-the-counter strips took 16 days to reach the level that trays reached in 7 days and an in-office treatment in a single day. The NHS describes laser whitening as one visit of 1 to 2 hours. Even then, part of the whiteness seen right after a session comes from drying and fades as the teeth rehydrate, as the next section explains.

Whether a lamp helps is disputed. The Canadian Dental Association’s 2007 statement says light makes in-office whitening faster but that the literature does not show whiter teeth; the NHS calls laser whitening faster and more effective than gel alone. A 2018 review of 21 trials found that light did not seem to improve the color change, whatever the peroxide concentration, and did not confirm the claim that it speeds it up.

References: [1] NHS · [2] CDA · [14] ADA · [15] Maran et al. · [16] Burki et al. · [17] Hatırlı et al. · [23] Auschill et al. 2005

Why teeth look whitest right after a session

Drying alone makes teeth look lighter for a while. In one trial of 20 people, a front tooth kept dry for 30 minutes changed shade and had not fully recovered 30 minutes after being wet again; in another study, of 30 people, almost every tooth was back within an acceptable difference after 24 hours. Neither study involved whitening, but the authors of the second advise judging a whitening result only once the teeth have rehydrated.

After in-office whitening with a lamp, one small trial, of 33 adults split into three groups, measured a significant rebound in color within 7 days. In its group treated with the lamp alone, without peroxide, teeth also looked less yellow right after treatment, and most of that change was gone by day 30: a photo taken right after a session can show more than will stay.

References: [16] Burki et al. · [17] Hatırlı et al. · [18] Kugel et al.

How to make whitening last: coffee, smoking, cleanings

According to the UK’s Oral Health Foundation, smoking and drinks such as tea, coffee and red wine can bring staining back more quickly. The one trial cited here did not show smokers losing more: among 30 smokers and 30 non-smokers whitened with trays, the two groups changed alike. At one year, a slight darkening disappeared on two of its three measures once a professional cleaning removed surface stains; by 30 months, both groups had darkened again, even after cleaning.

During and just after whitening, nothing shows that a strict “white diet” is needed: a 2024 review of five trials found no significant effect of colored food and drink, over one month of follow-up at most. Over the long run, brushing and regular cleanings at the dentist help keep the result, the foundation adds.

References: [19] Oral Health Foundation · [20] de Geus et al. (2015) · [21] de Geus et al. (2017) · [22] Hardan et al.

How to tell whether your whitening is holding

Since the color comes back gradually, compare like with like: the same phone, the same room, the same light, and never right after a session. No trial we found sets when to whiten again.

In Enamel, the plan follows the course on your strips’ or LED kit’s instructions, with breaks if you want them; after it, no more sessions: the daily habits and check-ins keep your shade and show it. A new cycle starts only if you choose one.

References: [4] Swift et al.