Clench your teeth. And now reeeelax!’ Professor Syed Haq is instructing me calmly, needle poised just millimetres from my skin. Then comes the sharp scratch. And another. Until six tiny injections have pierced the base of my jawline – three on each side.

Today, I’m having ‘masseter Botox’. Unlike regular Botox, this isn’t about smoothing fine lines or ‘freezing’ your forehead. It’s a treatment that has become well-known among stressed mid-lifers as a miracle cure for bruxism, the medical term for unconscious teeth-grinding and jaw-clenching, which affects one in four adults and often worsens during times of anxiety.

But that’s not why I’m having it – or it’s not the only reason. Among women in their 20s like me – sometimes described as the TikTok generation – the treatment is booming in popularity because of a newly-discovered side-effect.

By preventing the overuse of the masseter muscles, this type of Botox is supposed to produce a softer, more contoured jawline that can dramatically alter the silhouette of the face, particularly for those with naturally strong or bulky jaw muscles. So-called ‘jaw-slimming’ sculpts the face into a more feminine heart shape – or that’s the claim; less Brad Pitt and more Scarlett Johansson, with no surgery or downtime required.

I’ve long felt torn on the subject of Botox injections. In June last year, I wrote a piece for this newspaper about the boom in ‘preventative Botox’ – the idea that the jabs can slow down or prevent the formation of fine lines and wrinkles by relaxing facial muscles among women in their 20s and early 30s.

The procedure itself is quick. Each injection feels like a minor sting – less painful than I expected and no worse than a flu jab

Most of the women I interviewed were inspired by TikTok to smooth their foreheads and ‘preserve’ their youth – even though, like me, they barely had a wrinkle in sight.

In the end, however, I decided Botox wasn’t for me. Or ‘not yet’ in any case. I wasn’t convinced that it could slow ageing and not leave me looking frozen, with a rather startled expression, so I gave it a pass.

Then, five months ago, during a stressful day at work, I suddenly became aware of an odd tense sensation at the back of my mouth. I was grinding my back teeth together – not just a one-off clench, but an ongoing, involuntary grinding. Once I noticed it, I couldn’t stop.

I caught myself doing it constantly – at my desk, on the sofa reading, even walking to the shops. The worst was at night. I’d wake up with aching temples, a sore jaw and the kind of headache that painkillers wouldn’t shift.

I tried to de-stress (easier said than done). I looked into traditional treatments, like an ‘occlusal splint’ (a mouthguard you wear at night). But with NHS dental appointments more elusive than Glastonbury tickets, I was looking at around £400 to get one fitted privately.

And then, like a sign from the algorithmic gods, TikTok began feeding me videos of masseter Botox. Young women showing off striking before-and-after shots of their newly-sculpted faces, claiming it had cured their grinding and sharpened their jawlines in one fell swoop.

My appointment takes place at the Marylebone clinic of Professor Syed Haq – one of the UK’s most sought-after aesthetic doctor

Of course, one can’t help but wonder how many of these women are really struggling from clinical bruxism – and how many are simply using it as an excuse to slim their jawlines. A bit like when a Hollywood star reveals they’ve had surgery to ‘correct a deviated septum’ – and happens to emerge with a perfectly sculpted nose.

Flossie Clegg, a 24-year-old TikTokker from London, revealed she’d had the treatment after fans were speculating about the cosmetic work she’d had done.

‘I got Botox in my jaw,’ she said. ‘I did start getting it because I would grind my teeth and I actually didn’t realise it changes your face. I do really like the look aesthetically. I used to have a very strong, broad jaw – which I didn’t mind at the time but now that it has slimmed down my face, I like it.’

The hashtag #masseterbotox has so far been used more than 12,000 times on TikTok.

Some of the results are from women trying to ‘de-influence’ the treatment by warning of side effects – such as developing jowls, or a frozen smile. Even so, I decided to take the plunge.

My appointment takes place at the Marylebone clinic of Professor Syed Haq – one of the UK’s most sought-after aesthetic doctors – who runs the practice AM Aesthetics with his wife and aesthetician, Alex Haq.

Before a single needle is uncapped, I’m taken through a detailed consultation. We discuss my medical history, medication, and suitability for the treatment.

It turns out that, yes, I am suffering from bruxism – and I’m a prime candidate. Then Professor Haq asks me to repeatedly clench and relax my jaw while he observes. He holds up an iPad to analyse my profile and casually announces: ‘You have severe facial asymmetry.’

Charming!

His wife Alex quickly softens the blow: ‘There is more muscle thickening – or hypertrophy – of the masseter muscle on the right side.’

I’ve always noticed my jawline looks slightly stronger on that side, but I assumed it was my natural face. I never thought it could be corrected – or at least softened – by Botox.

Clara before she had the Botox, left, and after the treatment

Professor Haq explains his plan: 25 units of botulinum toxin type A on the right side, 20 on the left. The aim is to reduce the size of the more prominent muscle to create a more symmetrical, balanced look (while also preventing the grinding that’s been plaguing me).

Botox blocks nerve signals to the muscles, temporarily relaxing them. In the case of masseters – the muscles responsible for chewing – it means you’re no longer able to unconsciously clench or grind. The muscle shrinks from underuse, giving the jawline a softer appearance.

The procedure itself is quick. Each injection feels like a minor sting – less painful than I expected and no worse than a flu jab.

And although the toxin from the jab might take a few days to start paralysing the masseter muscles, Professor Haq tells me the relief may come not just from the Botox, but from the mechanical process of the needle breaking through the tense fibres of the muscle.

I wake up the next day with a dull, pulsing headache that sits behind my eyes. Professor Haq warned me about this. It’s caused by the temporalis muscle at the side of the head overcompensating for the weakened masseter. It’s unpleasant – but manageable with painkillers.

But what’s more surprising is the near-immediate relief in my jaw. Just 24 hours after the injections, my teeth grinding has almost entirely stopped.

For the first time in weeks, I wake up with no throbbing pain in my jaw. Sitting at my desk at work, it sits relaxed – rather than constantly clenching. And yes, I admit it – I begin to notice subtle changes in the mirror.

A few weeks later, the right side of my face looks slightly less bulky and my jawline less rounded. It’s a difference so slight that I

wonder if it might be placebo – but I’ll take it! However, as with all TikTok-viral beauty trends, backlash against the treatment has already begun.

Made In Chelsea star Sophie Habboo, 30, recently admitted that years of masseter Botox had left her with a ‘frozen’ smile. ‘It’s a really bad situation’, she said. ‘I look rank, to be honest.’

And 23-year-old YouTube star Olivia Neill last year revealed she had been left with numbness on one side of her jaw after getting the injections.

Reddit threads are also filled with cautionary tales from women claiming they developed jowls just months after having their masseters injected. Some say their faces look hollow or aged.

Dr Shereene Idriss, a respected New York-based dermatologist, posted a video earlier this year warning about the growing trend of cosmetic masseter Botox.

‘Medically, there is a purpose,’ she says. ‘But cosmetically, it can [wreck] your face. Once you bring that muscle down, [you get that] dreaded jowl.’

There’s no known method to reverse the effects of Botox. It can only naturally wear off over time, usually within three to four months – though Professor Haq tells me I could feel the effects for eight to ten months.

If you’re blessed with a strong bone structure, you’re going to be fine as you get older. But if you have a dainty jawline, your bone structure is not strong enough to hold up your face. That masseter muscle was giving the illusion of a better jawline.

So what’s the truth?

I certainly don’t have a strong bone structure – so I’ll be wary of the side-effects as the Botox continues working.

Alex Haq tells me it depends on the practitioner, the patient, and how often it’s done. While she would inject only after a medical assessment, many other clinics are reckless and will give injections to those who don’t need them.

Maybe I’ll need to think twice before doing it again, or tweak the dosage, or let the muscle regain some strength.

But, for now, waking up without an aching jaw feels like a luxury I didn’t realise I was missing. And I’d take pain-free mornings over a perfect profile any day.