Related

Method	Concentration	Contact	Notes
Whitening pen	Low	Poor — saliva washes it off	Mostly ineffective; convenient
Boil-and-bite tray	Low to moderate	Uneven	Gel escapes onto the gums
Custom-fitted tray (dentist-made)	Moderate	Excellent and even	The best home method by a wide margin
Chairside / in-office	High, with gum isolation	Controlled	Fastest; a clinical procedure
LED "accelerator" lamps	—	—	Evidence for added benefit is weak; the gel does the work

The custom tray is the thing worth paying for. A tray moulded to the teeth holds gel against the enamel evenly and keeps it off the gums — which is exactly what determines both how well it works and how much it hurts.

Home gels usually use carbamide peroxide, which breaks down slowly into hydrogen peroxide and urea. Roughly a third of a carbamide peroxide concentration is its hydrogen peroxide equivalent — so a 16% carbamide gel is approximately 5.5% hydrogen peroxide.

The slower release means longer wear times at lower peak concentration, which is gentler on the pulp. In-office gels use hydrogen peroxide directly at high concentration, with the gums isolated by a barrier.

The sharpest divergence in this catalogue, and it matters for anyone buying online.

	United States	European Union
Status	Cosmetic — FDA primary category (11) oral products	Cosmetic under Regulation (EC) No 1223/2009
Consumer peroxide limit	None specified. Gels of 10–44% carbamide peroxide are sold freely	0.1% hydrogen peroxide or equivalent — the maximum for direct sale to consumers
Higher strengths	Freely available	0.1–6% only via a dental practitioner, who must administer or supervise the first use; prohibited for under-18s

The EU restriction sits in Annex III and derives from the 2011 tooth-whitening amendment. In the UK, whitening above 0.1% by anyone other than a dental professional is treated as the illegal practice of dentistry, and enforcement has followed against beauty salons offering it.

High-strength gel bought online from another market may be illegal where you live, and an unregulated product may carry an uncontrolled concentration — which, with peroxide against gum tissue, is a genuine chemical burn risk.

• Yellow responds; grey does not. Tetracycline staining is the classic poor responder.
• Nothing whitens restorations. Crowns, veneers, composites and bonding do not bleach, and a course can leave them conspicuously darker. See a dentist before whitening if you have front-tooth restorations.
• Sensitivity and gum irritation are the two common effects, both dose-dependent and usually temporary. Potassium nitrate toothpaste before and during a course helps measurably.
• It fades, and it needs occasional top-ups.
• Untreated decay or gum disease must be dealt with first. Peroxide over an exposed cavity reaches the pulp directly and is painful.

Cosmetic in the US — FDA primary category (11) oral products. There is no premarket approval and no specified peroxide limit for consumer products, which is why the American and European shelves look so different.

The EU limits are as set out above. Neither jurisdiction treats home whitening as a drug.

Peroxide degrades continuously into water and oxygen, and heat accelerates it — carbamide peroxide gels are among the least stable products in this catalogue.

Refrigerate most home gels, keep syringes capped, and respect the printed date. A gel that no longer works has usually degraded rather than being the wrong product, and a swollen syringe has been generating gas and should be discarded.

• Oral Care — the shelf this sits on, and the rest of it.
• Cosmetics — what the label is legally allowed to say, and the full catalogue.
• The rest of Whitening — Whitening Strips.
• Whitening Toothpaste — the surface-stain alternative.
• Regulatory statements here follow the FDA and EU sources listed on Cosmetics, read 16 August 2026.