The legal position, plainly
In the UK, tooth whitening is dentistry. Only a dental professional may legally provide the products strong enough to whiten effectively, and it is illegal for beauticians, salons or kiosks to perform whitening [1]. Over-the-counter products are capped at concentrations too low to do much — which is why their results disappoint [2].
Why the examination comes first
Whitening gel does not distinguish teeth from problems. Decay, leaking fillings, exposed roots and gum disease all need treating before whitening — and crowns, veneers and fillings do not whiten at all, so a front tooth with a filling needs a plan, not just a gel. This is why a proper course starts with an examination, not a shade chart.
What actually happens
The usual approach is custom-made trays worn at home with a professional gel over a few weeks, checked by the practice as you go. Some sensitivity during treatment is common and settles. Teeth go on ageing, so the result fades gradually and can be topped up later.
The honest limits
Whitening lightens natural teeth — usually by a worthwhile, natural-looking amount. It does not produce the flat, paper-white of filters and screens, and chasing that shade is how enamel gets hurt. If a single dark tooth or old dental work is the real problem, bonding or a veneer may be the better answer — and an honest consultation will tell you that before you spend anything.
