Scarlett Johansson Is Back in London, But Her Most Painful Hollywood Makeover Was Dental

Back in 2006, when she was in the thick of her first big run of Hollywood films, Scarlett spoke about having her teeth whitened again and again for a role, and how much the sensitivity hurt.

That's the whole story on the record, and I'm not going to pad it out. We don't know exactly what products were used, how strong they were, how close together the sessions were, or whether anyone was supervising the process the way a UK dentist would today. Film sets run to tight schedules, and "we need your teeth whiter by Tuesday" is not a sentence any dentist enjoys hearing.

What I find interesting is that she didn't call it vanity, or regret. She just described it as painful. And that's a lot more relatable than most celebrity beauty stories.

Here's the science, short and sweet.

Whitening products usually use hydrogen peroxide, or something that releases it. The peroxide travels into the tooth and breaks down the stains inside, which is why teeth look lighter afterwards. It isn't just polishing the surface.

Your tooth isn't solid all the way through. Under the hard outer enamel is a layer called dentine, which is full of tiny channels leading towards the nerve in the middle of the tooth. When whitening gel gets busy in there, the nerve can get a bit irritable for a while. That's the sensitivity people feel: usually a sharp twinge with cold drinks or cold air, sometimes a dull ache.

Think of the nerve like a light sleeper. A bit of noise next door and it wakes up grumpy. Keep up the noise night after night, with stronger and stronger gel and no break in between, and it's going to be very grumpy indeed.

For most people, that sensitivity is temporary and settles down once the treatment stops or between sessions. Hospital patient information makes the same point: temporary sensitivity can happen. Temporary is the key word.

I can't diagnose Scarlett's teeth from a 20-year-old interview, and I won't try. But in my view, whitening tends to become really painful when one or more of these things happen:

• It's done too often, too close together. Teeth need time to settle. Back-to-back sessions to hit a deadline give the nerve no rest.
• The gel is too strong for the job. Stronger isn't always better. It's often just more uncomfortable.
• There's an underlying problem nobody checked. Decay, cracks, worn enamel, receding gums or leaky old fillings can all make whitening much more painful.
• The gel gets onto the gums. Badly fitting trays or poor technique can irritate or even burn the gums, which is a very different kind of pain.

This is why I always want to look at someone's teeth properly before they whiten. Not because I want to make it complicated, but because the most common cause of a horrible whitening experience is whitening teeth that weren't ready for it.

This is the bit a lot of people don't know, and I think everyone should.

In the UK, tooth whitening is dentistry. According to the General Dental Council, only registered dental professionals can offer or provide whitening treatment. The maximum strength of hydrogen peroxide a dentist can use for cosmetic whitening is 6%. Products sold over the counter can only contain or release up to 0.1% hydrogen peroxide.

The Northern Ireland government's guidance puts it bluntly: it's a criminal offence for anyone other than a registered dentist, or a dental hygienist, dental therapist or clinical dental technician working to a dentist's prescription, to carry out whitening. It also warns that products from non-dentists can cause burned gums, blistered lips or worse, and that products sold online often don't say what's actually in them.

So if a beauty salon, pop-up kiosk or bloke on Instagram offers to whiten your teeth, my advice is a firm no. It's not snobbery. It's the law, and it's your enamel.

If you'd like whiter teeth and you don't fancy suffering for your art, here's what I'd want you to know:

• Get checked first. Healthy teeth and gums are the starting point. Any decay or cracks need sorting before whitening.
• Go slow. Gentle, steady whitening over a few weeks is usually kinder than a rushed blast.
• Use custom trays. Trays made for your mouth keep the gel on your teeth and off your gums.
• Tell someone if it hurts. Sensitivity can often be managed by taking a break, spacing out sessions or using a sensitivity toothpaste. Don't just grit your (sensitive) teeth and carry on.
• Know what it won't do. Whitening works on natural teeth. Crowns, veneers and fillings won't change colour, so they may need replacing afterwards to match.
• Expect top-ups. Whitening isn't permanent. Tea, coffee, red wine and time all bring stains back eventually.

When it's done properly and legally, whitening is one of the more gentle cosmetic treatments out there. It doesn't involve drilling or removing any tooth. The main side effects are usually temporary sensitivity and some gum irritation, and both tend to settle.

The problems come with shortcuts: unregulated products, unknown chemicals, too much too often, and nobody checking the teeth first. That's where people end up with burns, damaged enamel or the kind of pain Scarlett described.

If you want to compare whitening with other ways people change their smile, I've also written about the two treatments Maura Higgins had, Invisalign and bonding, which is a very different route.

Does teeth whitening always hurt? No. Some people feel nothing at all. Others get temporary sensitivity, usually twinges with cold. Severe pain is a sign to stop and get your teeth checked.

How long does whitening sensitivity last? For most people it settles within a short time of stopping treatment or between sessions. If it doesn't, see a dentist.

Can I whiten my veneers or crowns? No. Whitening only works on natural teeth. If you have veneers, crowns or tooth-coloured fillings at the front, they'll stay the same shade.

Are home whitening kits safe? Over-the-counter kits are legally limited to very low strengths. The real worry is products bought online that don't say what's in them. If you can't tell what's in it, it doesn't go in your mouth.

Scarlett Johansson can still light up a London red carpet twice in one day, and her smile is part of that. But her story is a useful reminder that a camera-ready smile shouldn't come at the cost of weeks of pain.

Whitening done properly is gentle, gradual and supervised. If it feels like torture, something's gone wrong, and that's your cue to stop, not to push through for the sake of a premiere.

This article is general information based on what Scarlett Johansson has said publicly. It is not personal dental advice. Scarlett Johansson, the BFI London Film Festival and the films mentioned have no connection with this article.