Hismile: Can it really brighten your teeth?

Unfortunately, white teeth tend to come at a cost. Professional teeth whitening can be as much as $500.

But over-the-counter whitening products offer a cheaper solution to a costly visit to the dentist. Many of them now contain alternatives to typical whitening ingredients, promising to minimise pain and sensitivity.

What are Hismile’s PAP+ whitening strips?

Hismile is an Australia-based at-home dental care and teeth whitening company. I first found out about it on social media where it has millions of followers. You can find its advertising in all corners of the internet, from Facebook to TikTok.

The first time I saw one of its ads, I was almost fooled into thinking it was an independent review. One video in particular had me hooked.

“I gave into TikTok and tried the famous teeth whitening strips. I’m sure you’ve seen this online, but apparently these are the best whitening strips for your teeth …”

So, I bought them. At $30, it set me back about $4.30 for an application.

Two weeks later, they arrived at the office in an eye-catching pink sachet. The “dentist-backed” strips boast “instant whitening” with no “nasty side effects”. Hismile claims this is because they don’t contain hydrogen peroxide as an active ingredient, but instead use a “pain-free” alternative.

Our ‘in-mouth’ trial

We wanted to see how Hismile’s PAP+ strips performed inside real mouths, so we based our trial on how a consumer would use the product at home. Six people from the Consumer NZ office offered up their pearly whites for the trial.

We took photos in the same room under the same lighting to control variables. Lighting varied only with changes in natural light outside the office. We took photos before and immediately after using the strips. We’d been advised that the shade achieved might settle down after a few days, so we also took a photo 7 days after whitening.

Our triallists all followed the same instructions, as listed on the product and Hismile's website.

1. Thoroughly dry teeth, peel off the long strip and apply sticky side to top teeth
2. Press strip down firmly and fold over back of teeth to secure.
3. Repeat for short strip on bottom teeth.
4. Allow 30 minutes for whitening treatment.
5. After, remove the strips and rinse mouth with water.

The strips’ safety instructions warn against use in children and against swallowing a strip. They also warn not to use in the eye area and to consult with a doctor before use if you’re pregnant or breastfeeding.

Each triallist filled out a form and ranked their experiences on a scale of 1 to 10: 1 being low and 10 being high.

We included a question about pain, separate to sensitivity in our survey. Everyone experiences sensitivity differently and judging by sensitivity alone may not capture experiences accurately.

The results

Ease of use: 6/10. They don’t stick brilliantly (even after drying my teeth).

Free from pain: 10/10.

Free from sensitivity: 9/10. There’s no pain, but it feels like I’ve layered toothpaste onto my teeth and let it sit. It does feel like it’s hitting my bones and it’s a bit achy.

Whitening effect: 1/10.

Would you say the strips worked instantly? No.

Would you use the strips again? No.

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Ease of use: 7/10.

Free from pain: 9/10.

Free from sensitivity: 9/10.

Whitening effect: 1/10.

Would you say the strips work instantly? No. If anything, they made my teeth look more yellow, perhaps because they only whitened the front and not in between, increasing the contrast.

Would you use the strips again? No, and I’d like a refund.

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Ease of use: 5/10. The top strip went on like a dream, but the bottom one was a fail and wouldn’t stick.

Free from pain: 10/10

Free from sensitivity: 10/10.

Whitening effect: 3/10. Maybe they’re whiter but maybe it’s in my head?

Would you say the strips work instantly? Maybe a subtle change, minimal though.

Would you use the strips again? No.

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Ease of use: 5/10.

Free from pain: 8/10.

Free from sensitivity: 4/10. It hurt when I rinsed my mouth after and if I breathed in.

Whitening effect: 3/10.

Would you say the strips work instantly? Yes, people said they did.

Would you use the strips again? No. I’ve used some before that worked much better. The actual strip is thin and slips during the 30 minutes on.

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James, product test team leader | Kaiārahi Kapa Whakamātau Hautaonga

Ease of use: 6/10. I felt like my saliva production kicked into overdrive and 30 minutes feels like an age to go without snacks or a drink. Way stickier than I thought it would be.

Free from pain: 10/10.

Free from sensitivity: 8/10.

Whitening effect: 1/10.

Would you say the strips work instantly? No.

Would you use the strips again? No, I get cheap, AliExpress vibes.

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Jocelyn, people and development manager | Kaiwhakahaere Tangata, Whakawhanake

Ease of use: 3/10.

Free from pain: 9/10.

Free from sensitivity: 9/10.

Whitening effect: 2/10. It’s hard to score whitening! If they’re whiter, I’m not sure that it’ll last.

Would you say the strips work instantly? There was a slight change over the 30 minutes.

Would you use the strips again? No.

Averaged results

Do the claims check out?

Instant

Only two of our triallists, Jocelyn and Molly, agreed the strips worked instantly. Jocelyn noted a slight change happened over 30 minutes, but we’re not convinced it’s fair or truthful to call 30 minutes instant.

In the UK, the British Advertising Standards Authority ruled that Hismile’s claim that teeth could be whitened in just 10 minutes was misleading.

As of November 2023, “instant” is no longer a claim on Hismile’s strips.

Whitening

Only half of our triallists noticed their teeth were whiter following the treatment. Only Jocelyn, Gemma and Molly said they experienced any whitening effect. Both Jocelyn and Gemma weren’t convinced it was significant.

We thought in most cases it was difficult to tell the difference between the before and after photos. Frank thought the treatment made his teeth look less white overall.

Sensitivity-free

Three of our triallists experienced sensitivity. Molly had the worst, but Abby and James also noticed sensitivity.

Pain free

One of our triallists, Molly, ranked free from pain as 8/10. Molly also experienced the worst sensitivity and the biggest whitening effect.

Dentist-backed

We asked Hismile if it could provide a list of dentists that back its whitening strips. It initially refused to release any names on privacy grounds. But when we asked if it could substantiate its claim that the product was dentist-backed in any way, it gave us the names of three Australian dentists and one New Zealand dentist.

As of November 2023, “dentist-backed” is no longer a claim on Hismile’s strips.

Study finds PAP whitening worse than saline

A 2019 study by the British Dental Association compared several over-the-counter whitening products with a variety of active ingredients, including one with phthalimidoperoxycaproic acid (PAP).

The study found the PAP product resulted in a significant reduction in microhardness. It also caused surface alterations to the tooth. However, the product also contained citric acid, which the authors state may have been the cause of the surface alterations.

The study also found that the PAP product caused the second least amount of whitening of the products tested, and was worse at whitening than saline alone (the control for the study).

A 2021 study found a new formulation of PAP, which it called PAP+, didn’t alter the enamel structure of the tooth. The authors of that study were employed by Hismile at the time.

A 2023 study compared the effectiveness of over-the-counter whitening agents. It showed that the greatest whitening effect achieved by over-the-counter products was the lifting of surface stains. Only hydrogen peroxide could further whiten enamel. The study found that PAP (not PAP+) didn’t alter enamel structure.

One of the study’s authors went on to develop a whitening toothpaste and set containing PAP.

Another 2023 study came to the same conclusion as the 2021 study, that PAP+ didn’t alter enamel structure.

However, these studies took place in controlled, laboratory environments rather than inside an average human mouth. How PAP and PAP+ interact with all the usual variables inside a mouth, an acidic diet or past whitening for instance, is still largely unknown.

A 2017 study looked at how a single application of a PAP-based product might affect teeth. It found that PAP was an effective bleaching agent but didn't test impacts on microhardness or demineralisation. The study admitted the product "may potentially cause irreversible damage if used on a long-term basis." It was also performed under supervision of a dentist.

Ultimately, outside of a lab, results have the potential to vary and blanket statements that PAP doesn’t cause sensitivity might be inappropriate or potentially misleading.

The active ingredients in over-the-counter whitening

PAP

What is it? PAP is short for phthalimidoperoxycaproic acid. It is a chemical oxidiser.

The + in the Hismile product name represents hydroxyapatite and potassium citrate. Hydroxyapatite is a form of calcium found in tooth enamel. It can help prevent mineral loss and enamel softening. Potassium citrate is used as a desensitising ingredient.

What does it do? It bleaches the tooth by breaking down stain molecules.

How much is allowed in over-the-counter products? PAP and PAP+ are not currently regulated for use in New Zealand in over-the-counter tooth whitening products.

What are the potential harmful effects? The European Union warns PAP is “very toxic” to marine life. It can cause serious eye damage and it’s flammable if heated.

Hydrogen peroxide

What is it? A chemical oxidiser.

What does it do? It bleaches the tooth by breaking down stain molecules.

Dr Mo Amso, chief executive of the New Zealand Dental Association explained hydrogen peroxide was a trusted whitening agent in the industry. “Hydrogen peroxide is the standard material used for dental bleaching.”

How much is allowed in over-the-counter products? No more than 7% in New Zealand.

In the EU, oral hygiene products containing more than 0.1% hydrogen peroxide can’t be sold over the counter.

Dr Amso said regulation was important as hydrogen peroxide “could have harmful effects if not used appropriately.”

What are the potential harmful effects? Irritation of the gums, mild to significant chemical burns, damage to the enamel and tooth sensitivity.

“It infiltrates into the dental structure to remove staining and can cause demineralisation. The higher the concentration, the greater the potential for gum irritation and sensitivity,” said Dr Amso.

Which chemical is safer?

PAP and hydrogen peroxide are distinct chemical oxidants that can both act as bleaches.

But while Hismile claims PAP is safer for the enamel than hydrogen peroxide, Associate Professor Dr Nigel Lucas, head of chemistry at the University of Otago, said it's not black and white.

According to Dr Lucas, PAP might be just as harmful as hydrogen peroxide on the teeth.

“In the presence of water [PAP] can decompose to generate hydrogen peroxide and a carboxylic acid,” Dr Lucas said. As normal saliva is around 99% water, this chemical reaction might happen while using the PAP+ strips, he adds.

Hismile recommends users wipe their teeth dry, but as our triallist James found, saliva production doesn’t stop while the strips are in place. Further, Hismile’s instructions to rinse the mouth with water after use might also provide an opportunity for the reaction to occur.

PAP’s effect on teeth

Dr Amso said not much is known about PAP’s effects on the teeth. “There’s a lack of regulation which means it could be easily sold in the market without any oversight.”

Dr Amso said any claims that a product can instantly whiten may be challenging to verify.

“If it does work instantly, the result could be quite extreme over the first hour. Over the next few days the shade stabilises.

“There’s a possibility something could whiten shortly after application. But it may be misleading to say that’s the shade you end up with moving forward.”