What over-the-counter strips contain
Whitening strips are thin strips coated with a gel that you place on your teeth. According to the American Dental Association (ADA), most rely on peroxide: hydrogen peroxide, or carbamide peroxide, which releases it.
In the European Union, a 2011 directive sets two levels. Up to 0.1% hydrogen peroxide, present or released, a product can be sold over the counter. Between 0.1% and 6%, it can only be sold to dentists: the first session of each cycle takes place at the practice, the rest can be done at home with the product the dentist provides, and never under 18.
Products sold elsewhere do not necessarily follow these limits; in the United States, follow the instructions on the box. Before using strips bought abroad, talk to your dentist. A “peroxide-free” label means the product uses another agent: its ingredients are listed on the pack.
Hydrogen peroxide: three levels
- Up to 0.1%Over the counterConsumers can buy and use the product directly.
- 0.1% to 6%Through a dentistSold to dentists only. The first session of each cycle at the practice, the rest possibly at home. Never under 18.
- Above 6%Not allowedAbove this level, a tooth whitening product is not allowed.
References: [1] Directive 2011/84/UE · [2] CED · [4] ADA
Before or after brushing?
Don’t apply strips straight after brushing. The manufacturer Crest advises against it to avoid gum irritation and recommends letting some time pass between brushing and applying them. After the session, you can brush gently.
Everything else depends on the product: wear time, number of sessions, what to eat and drink afterwards. Two brands can give different instructions; the ones on your box take precedence.
| Step | What you do | Why |
|---|---|---|
| Before | Read the instructions and set a timer. | Wear time differs from one product to another. |
| Applying | Place the strip in front of a mirror, in good contact with your teeth. | A strip that slips can spread onto the gums. |
| During | Keep the strip on for the stated time, no longer. | Wearing it longer is not part of the instructions. |
| After | Remove the strip, then brush gently if you like. | Gentle brushing after a session is fine. |
References: [6] Crest
How many sessions, and how often?
The instructions give the length of a cycle and the number of sessions per day. Don’t double up to go faster: for its own strips, Crest advises against using more than two upper and two lower strips a day.
The 2018 Cochrane review, covering 71 trials and 3,780 adults, found whitening compared with placebo over periods of 2 weeks to 6 months. The certainty of the evidence is low to very low, and no concentration, wear time or method could be identified as the best.
So nobody can promise you a number of shades or a date. A pace you can keep, with breaks when you need them, is better than a forced cycle.
References: [3] Cochrane · [5] Crest
Sensitive teeth: when to take a break
Sensitivity is the most common effect. According to the ADA, mild to moderate, temporary sensitivity affects up to two-thirds of people in the early stages of whitening. It often appears after two to three days. The Cochrane review also reports gum irritation, more common with higher concentrations and usually mild and temporary.
If clear sensitivity or gum discomfort develops, Crest suggests switching to a session every other day, then stopping if the problem continues. If your teeth are already sensitive before you start, or the discomfort lasts, that’s one for a dentist to look at.
If your teeth become sensitive
- Sensitivity appearsOften after two to three days of sessions. It is usually mild and temporary.
- Space out sessionsOne session every other day, staying within your product’s instructions.
- It continues: stopStop the sessions. That’s one for a dentist to look at.
References: [3] Cochrane · [4] ADA · [5] Crest
Crowns, veneers and white spots
Strips only lighten natural teeth. A crown, veneer or composite on a front tooth keeps its color, which can create a visible difference. Talk to your dentist before you start.
White spots can appear just after a session. According to Crest, they come from a loss of water from the enamel, are not harmful and go away. Wait before judging the color: a photo taken straight after a session does not show your usual shade.
Judging the result without fooling yourself
To see whether the strips are working, compare photos taken in the same conditions: same phone, same room, same light, and never straight after a session. A photo taken under a different lamp is enough to suggest a change.
The result is not permanent: according to the ADA, it depends on your habits, and coffee, tea or tobacco stain the surface again over time. A glass of water after a drink that stains is still the simplest habit.
References: [4] ADA
Sources and further reading
- Directive 2011/84/UE du Conseil du 20 septembre 2011 — produits de blanchiment des dents (EUR-Lex)
- Council of European Dentists — Lignes directrices pour interpréter la directive 2011/84/UE (2012)
- Cochrane — Home use of tooth whitening products (revue systématique, 2018)
- American Dental Association — Whitening
- Crest — Whitening FAQs (fréquence, sensibilité, taches blanches)
- Crest — Can I brush my teeth before or after using Whitestrips?
General information for adults, prepared by the Enamel team from the sources above. Not clinically reviewed. Ask your dentist for advice specific to your teeth. Our editorial approach.