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Mouthpieces that glow blue are one of the most common at-home teeth whitening light products sold online. But what whitens teeth is the peroxide in the gel, not the light. This article reviews the research on the role of light, the limits on bleaching agents, side effects and who should see a dentist first.

Why teeth become discoloured

According to the American Dental Association (ADA), there are two groups of causes:

• Extrinsic stains (on the surface): mainly habits such as smoking and strongly coloured food and drink; Vietnam's Vinmec hospital (Vietnamese) adds coffee, tea and red wine.
• Intrinsic stains (inside the enamel or dentine): genetics, fluorosis, ageing, tetracycline antibiotics in childhood, tooth decay or amalgam fillings.

The ADA says whitening can work on both types of stain, but only natural teeth get lighter; tooth-coloured restorations do not.

How tooth whitening works

• The active ingredient is hydrogen peroxide or carbamide peroxide (which releases about one-third of its content as hydrogen peroxide) — a strong oxidising agent that permeates the hard tissues of the tooth (ADA).
• Dentist-prescribed home trays typically use 10–38% carbamide peroxide gel (ADA).
• A light, including blue light, contains no bleaching agent. Lights in in-office systems are designed to speed up the process; whether they actually do is a question for the research.

Does an at-home teeth whitening light work better? What the research says

• He et al. (2012): a review of 11 studies of in-office bleaching. With 25–35% hydrogen peroxide gels, light made no difference; with 15–20% gels, light gave a better immediate result, though the authors said more research was needed. The light groups had more tooth sensitivity. PubMed
• Maran et al. (2018): pooled 21 randomised trials and found no significant difference in colour change or sensitivity with or without light, regardless of gel concentration. Certainty of evidence ranged from moderate to very low depending on the outcome. PubMed
• Maran et al. (2019): a network meta-analysis of 28 studies found no type of light activation better than bleaching without light, for both high- and low-concentration gels. Only 9 studies were at low risk of bias. PubMed
• Reis et al. (2026): a narrative review by the same group of authors concluded that light gives no additional clinical benefit, and that over-the-counter products do not replace dentist-supervised bleaching. PubMed
• Lights used at home: Shekari et al. (2025) tested 84 extracted teeth and found that over-the-counter gels used with their LED lights changed colour more than the gels alone. This was a laboratory study, not a study in people. PubMed

In short, the clinical evidence — mostly from in-office bleaching — shows that light adds little or nothing; data on lights used at home are still scarce. Results depend mainly on the gel and how it is used. Leaving gel on longer than recommended does not noticeably whiten more but may increase sensitivity (Reis et al.).

Peroxide limits for products you use yourself

According to the UK's General Dental Council (GDC), the rules that stem from EU Directive 2011/84/EU are:

• Less than 0.1% hydrogen peroxide: can be sold freely.
• 0.1–6%: may only be sold to dental practitioners; an examination is required, and the first use of each cycle must be done or supervised by a dental practitioner; not for anyone under 18.
• Above 6%: prohibited for cosmetic purposes.

If you buy a gel to use with a light mouthpiece, check the concentration on the label and ask a dentist about the right concentration and regimen, as Tam Anh General Hospital (Vietnamese) advises. Higher concentrations may whiten faster at first but increase side effects without improving the final result (Reis et al.).

Side effects and who should not whiten at home

Common side effects

• Temporary sensitivity and gum irritation are the most common (ADA). Mild to moderate sensitivity can affect up to two-thirds of users early on and usually passes quickly; gum irritation is usually caused by poorly fitting trays or applying gel incorrectly.
• The NHS (UK) also lists teeth sensitive to cold or sweet things, sore gums or throat, and white patches on the gums.
• Overuse can cause prolonged sensitivity, gum burns or enamel damage (Tam Anh).

Who should not whiten their teeth at home

• Children and teenagers: the NHS does not whiten teeth for anyone aged 17 or younger; EU rules bar 0.1–6% products for under-18s. Vietnamese sources give a cut-off of under 16 (Vinmec) or under 18 (Tam Anh).
• Pregnant or breastfeeding women (Vinmec, Tam Anh).
• People with untreated decay, gum disease, worn tooth necks or exposed roots: get these treated first (Vinmec).
• People with sensitive teeth or gums, or thin teeth (Tam Anh); anyone with a past allergy to bleaching agents (Vinmec).
• People with crowns, veneers or fillings on front teeth: restorations do not change colour (ADA), so they may no longer match. The NHS does not recommend whitening if you have crowns, dentures or implants.

See a dentist first, and keep teeth white afterwards

• The ADA advises consulting a dentist to decide whether whitening is right for you. Vinmec notes that before bleaching, dentists usually remove tartar, fill worn tooth necks and treat sensitivity, and that home bleaching should also be guided and supervised by a dentist.
• The NHS says whitening at beauty salons, or with kits bought from pharmacies or online, does not work as well and may harm teeth and gums.
• To keep teeth white: cut down on coffee, tea and red wine, and do not smoke (Tam Anh); for about 2 weeks after bleaching, drink coloured drinks through a straw (Vinmec). For whitening done by a dentist, the NHS says the effect may last around 3 years if you follow your dentist's advice.

The Inmax M245 teeth whitening device

The M245 is a U-shaped mouthpiece that emits blue light, red light or both. It comes in a version with a 400 mAh battery and USB-C charging and a version without a battery, rated at 1.4 W. It is a light device used with a whitening gel and routine as instructed — the light itself is not a bleaching agent. Inmax does not promise a specific number of shades, because results depend mainly on the gel, the condition of your teeth and how you use it. See a dentist and ask which gel suits you before you start.

Browse the teeth whitening range, compare products or contact Inmax; resellers can see our dealer policy.

Frequently asked questions

Does an at-home teeth whitening light work?

The whitening comes from the peroxide gel. Current reviews show that light adds little or nothing; research on lights used at home is still limited.

What is the red light on the M245 for?

The M245 has a red mode and a combined mode, but Inmax makes no claim about any treatment effect of red light. Use it according to the instructions and your dentist's advice.

Will crowns and fillings get whiter?

No. Restorative materials do not change colour, so they may stop matching your natural teeth after whitening; ask your dentist first.

This article is for general information only, compiled from the sources linked above; it does not replace diagnosis or advice from a dentist.