Tooth Whitening Products: Strips, Toothpastes, Pens and What to Check Before Use

What Do Whitening Products Actually Change?

The whitening products on sale do not all work the same way. There are three distinct mechanisms, and telling them apart determines what can reasonably be expected from a product.

• Chemical whitening: Hydrogen peroxide or carbamide peroxide breaks down coloured molecules within enamel and dentine. This is the only mechanism that lightens the tooth's own colour.
• Mechanical cleaning: Abrasive particles scrape away extrinsic deposits from the surface. This does not lighten the tooth; it removes what sits on it.
• Optical effect: Substances such as blue covarine leave a thin film on the tooth surface so the shade appears less yellow to the eye. This is not a real colour change and washes away.

The word "whitening" on a package says nothing about which mechanism is at work. This distinction explains why the product groups below give such different results.

The Limit Regulations Set on Open Sale

Cosmetics legislation explicitly limits the hydrogen peroxide content of tooth whitening products. For oral and dental care products containing hydrogen peroxide, or releasing it during use:

• Below 0.1%, the product may be sold freely.
• Between 0.1% and 6%, the product may be sold only to dental practitioners and is used on a dentist's recommendation. The packaging must state the peroxide concentration and carry the warnings "not to be used by persons under 18" and "to be sold to dental practitioners only".

The practical consequence is this: a product sold directly to you, on a shelf or online, cannot lawfully contain more than 0.1% hydrogen peroxide. That concentration is low for producing a marked change in the tooth's own colour. Most openly sold products therefore deliver surface cleaning or an optical effect rather than chemical whitening.

If a product is sold directly to you and nevertheless states a high peroxide concentration, there are two possibilities: the figure is not accurate, or the product is being sold contrary to the regulations. From your side both lead to the same place — you do not know what you are using.

Whitening Toothpastes

Whitening toothpastes are mostly pastes with a raised proportion of abrasive particles. They can make a difference to surface discolouration from tea, coffee and smoking; they do not lighten the tooth's natural colour.

The abrasiveness of a paste is expressed by a value known as RDA. Using a high-RDA paste twice a day with a hard-bristled brush and firm pressure can, over time, cause loss of tooth structure on the enamel surface and particularly near the gum margin. Loss in this area is linked both to sensitivity and to cervical tooth wear.

Charcoal (Activated Carbon) Pastes

Pastes containing activated carbon belong to the abrasive group. They may lift surface stains, but their particle structure is not standardised and fluoride-free formulations are common. Switching to a fluoride-free paste means, for someone at risk of decay, trading the pursuit of whiteness for caries risk.

Whitening Strips

Strips are made by coating a flexible band with a gel containing a low proportion of peroxide; the band is pressed onto the teeth and left in place for a set time. Because of the concentration limit on open sale, the chemical effect is limited. The real problems arise in use.

• The strip does not match the arch. A flat band does not seat fully on a curved dental arch. Where teeth sit forward or back, the gel does not contact every surface equally, and the result is a patchy shade.
• Gel overflows onto the gums. When peroxide contacts gum tissue, blanching, a burning sensation and temporary sensitivity may occur.
• It does not reach between the teeth. Strips act only on the front surfaces; the contact areas stay as they were.
• Exceeding the time is common. The idea that "leaving it longer makes teeth whiter" does not increase the colour gained; it increases sensitivity.

Paint-on Gels and Whitening Pens

Pen or brush-tipped products are designed to apply gel directly to the tooth surface. Two further problems arise in this group.

The first is contact time. The gel remains as a thin layer on the tooth; it is diluted by saliva and wiped away within a short time by lip and tongue movement. The contact time peroxide needs in order to act is not reached this way.

The second is uneven application. Gel applied by eye does not reach every tooth in the same thickness. The front surface of one tooth may lighten while its neighbour stays as it was, and the resulting difference can draw more attention than the original discolouration.

Some products in this group contain only a covering agent rather than peroxide. In that case the effect resembles make-up: it comes off with brushing, eating or drinking.

Pharmacy Products and Ready-Made Tray Kits

Being bought at a pharmacy does not change a product's content; the same 0.1% limit applies to the product on the pharmacy shelf. What the pharmacy provides is a traceable labelling and import chain. That is not trivial, but it does not increase the product's effect.

Ready-made tray kits raise a further issue. A one-size tray, not made for the individual, does not seat fully on the dental arch. In a tray that does not seat, gel is not held against the tooth surface; it leaks onto the gums and the floor of the mouth. Home whitening carried out through a clinic is therefore done with a tray made from the person's own impression, with its edge trimmed so that it does not cover the gum.

Before buying a product, asking your pharmacist about its content and peroxide concentration gets you an answer faster than turning the box over to read the small print.

Products of Unknown Content Sold Online

The real risk is concentrated in products sold through overseas marketplaces or social media without local labelling, manufacturer details or an ingredient list. The main harms are as follows.

1. Unknown Concentration

If the packaging does not state the concentration, or the stated figure cannot be verified, you cannot know how much peroxide you are exposed to. Uncontrolled use of a high-concentration gel can cause surface roughening of the enamel, prolonged sensitivity and chemical burns to the gums.

2. Products Containing Chlorine Dioxide

Some products use chlorine dioxide instead of peroxide and are acidic. An acidic environment dissolves enamel; part of the "whiteness" obtained comes from the roughened enamel surface reflecting light differently. A roughened surface then stains faster, and this loss does not reverse.

3. Misleading Promotional Images

Comparison images on product pages can be altered through lighting, angle and editing. Forming an expectation from an image tells you nothing about the product's real effect.

4. Risks Beyond the Mouth

Swallowing gels of unknown content can cause nausea and throat irritation. Fruit-flavoured products in reach of children carry a separate risk of accidental ingestion.

5. Home Kits With a Light

In kits that include a blue light source, the role of the light is limited; it is the gel that changes the colour. The light does not compensate for the gel's low concentration.

What the Search for Cheap Whitening Costs the Teeth

The search for a cheaper route to whitening often ends up in the kitchen. What these methods share is that the loss they cause to the tooth does not reverse.

• Baking soda: Abrasive. Used with a brush and firm pressure, it thins the enamel surface and the thin layer of enamel at the gum margin.
• Lemon juice, vinegar, apple cider vinegar: Acidic, and they dissolve enamel. Used together with baking soda, abrasion and acid act at the same time — one of the more demanding combinations for enamel.
• Salt, ash, ground shell: Particle size is uncontrolled and leaves scratches on the enamel surface.
• Hydrogen peroxide solution: The wound-care solution sold at pharmacies is not designed for whitening inside the mouth. Its concentration and contact time are uncontrolled, and it can burn gum tissue.

The impression that these methods work in the first days comes from the scraping away of surface deposits. Once the deposit is gone, if the practice continues, what wears away is the enamel itself. Enamel does not regenerate; thinned enamel reveals the dentine beneath, and dentine is yellow. After a while, therefore, the tooth begins to look yellower than it did at the start.

Sensitivity also increases on worn enamel. In people presenting with this picture, the cause of the sensitivity and the extent of structure loss are assessed first; whitening does not come into question at that stage.

What Products Do Not Change

There are situations in which no whitening product has an effect. Knowing them can spare you futile attempts.

• Fillings, crowns and veneers do not whiten. Composite, porcelain and zirconia are unaffected by peroxide. If natural teeth lighten, the colour difference against restorations becomes more obvious. For someone with restorations in the front region, renewing the restoration may follow whitening, which is why the two are planned together from the outset.
• Tartar and hard deposits do not dissolve. Whitening gel does not remove deposits, nor does it reach the tooth surface beneath them. If the discolouration is caused by deposits, the step to take is dental cleaning.
• Darkening of a single tooth is a different picture. Products applied from the outside do not affect a tooth that has darkened from within after trauma or root canal treatment. In that case whitening from inside the tooth is assessed; the detail is in the article on a tooth that darkens after trauma.
• Decay and fractures are not covered over. An area taken for discolouration may be decay. A whitening product does not conceal this, but it does delay its recognition.
• Developmental and medication-related discolouration is resistant. In certain discolourations formed during tooth development, the effect of externally applied whitening remains limited.

What to Look For on the Package Before Buying

If you have decided to use an openly sold product, check whether the packaging carries the following:

• An ingredient list in your own language, with manufacturer or importer details
• A stated concentration of hydrogen peroxide or carbamide peroxide
• An expiry date and batch number
• Clear instructions on duration and frequency of use

If any of these is missing, the information about the product is incomplete. Furthermore, if you have an existing filling, crown, gum recession or known sensitivity, asking your dentist before using the product can spare you a situation that later needs correcting.

When to See a Dentist

Product use should be stopped and an assessment made in the following situations: sensitivity that does not settle within a few days, blanching or an ulcer on the gum, marked darkening of a single tooth, a patchy shade, bleeding when brushing, or stains and lines remaining after use.

Attempts made without establishing the cause of the discolouration are not only fruitless; they also delay recognition of an underlying problem. You can arrange an appointment for assessment through the contact page. Information on the methods used at the clinic is on the tooth whitening page, and the period after treatment is covered in eating after whitening.

This article is for general information purposes and does not replace a clinical examination. The cause of discolouration and the approach suitable for you can only be determined by your dentist after clinical and, where necessary, radiological evaluation.