If you have swallowed a small amount of take-home teeth whitening gel, the usual result is a bitter taste, a sore throat or mild nausea, because the peroxide breaks down into water and oxygen in the stomach; gel left on your lips or gums causes a white, stinging patch that typically heals within a few days. Both usually trace back to too much gel in the tray. A medical toxicology reference reports that hydrogen peroxide solutions between 1% and 9% are generally benign when swallowed, which covers take-home kits. Here is what to do, and when to ring the Poisons Information Centre on 13 11 26.
Written by Dr James Tran, BDent (University of Sydney), MICOI, GradDip (Oral Implants), general dentist at Lumi Dental in Melrose Park.
The short version
- Take-home gels are typically 10 to 16% carbamide peroxide or up to 6% hydrogen peroxide. A swallowed smear is unpleasant, not dangerous.
- Spit, rinse your mouth and sip water. Do not make yourself vomit.
- Ring 13 11 26 (24 hours, Australia wide) if a child has swallowed any gel, a whole syringe or more has gone down, the gel is in-chair strength, or there is vomiting or pain. Call 000 for breathing difficulty.
- A white patch on the gum or lip is a superficial chemical burn. Wipe the gel off, rinse, and it usually settles in a few days; see our article on gum irritation after whitening.
- Load the tray with a small dot per tooth and wipe away anything that squeezes out. Overfilling causes most of these problems.
- Keep gel away from children and pets.
What is in the gel, and why the strength matters
Take-home whitening uses one of two active ingredients. Carbamide peroxide breaks down in the mouth into urea and hydrogen peroxide; research published in the Dentistry Journal reports that a 10% carbamide peroxide gel yields about 3.5% hydrogen peroxide, so a 16% gel delivers roughly 5 to 6%. In-chair gels in the published studies run from about 32 to 40% hydrogen peroxide, and are applied only by a dentist with the gums protected.
In Australia the ACCC has told suppliers that kits above 6% hydrogen peroxide or 18% carbamide peroxide are unsafe for home use and should not be sold to consumers; stronger gels are for registered dental practitioners only. The ACCC acted after reports of injuries from over-strength kits, including chemical burns to gums and the mouth, and blistering or ulceration of the mouth and throat. Our articles on whitening gel strengths and whether at-home whitening kits are safe go further.
Swallowed gel: what happens inside
Hydrogen peroxide breaks down quickly into water and oxygen. The medical reference StatPearls notes that it generates roughly ten times its own volume in oxygen gas, which is why a swallowed mouthful causes foamy burping, bloating and nausea. For solutions between 1% and 9% it describes accidental ingestions as generally benign, and says that people who swallow low-strength peroxide and have no symptoms can usually be watched at home.
A tray overfill is a fraction of a millilitre, and a whole syringe of take-home gel is a few millilitres at most. The same reference notes that serious injury follows very large volumes of low-strength solution, more than about 150 mL, or solutions of 10% or more, which are corrosive. A take-home kit cannot reach either threshold in one sitting; in-chair gel, or a syringe-full in a small child, is a different matter.
What I tell patients: spit, rinse well, drink a glass of water, and give it an hour. Do not make yourself vomit. The NSW Poisons Information Centre's first-aid advice for any swallowed poison is not to induce vomiting and to ring 13 11 26 rather than wait for symptoms.
The single rule: if you are unsure, ring 13 11 26
The Poisons Information Centre answers 24 hours a day, Australia wide, from The Children's Hospital at Westmead, a short drive from Melrose Park. Ring straight away if a child has swallowed gel or chewed a strip, if an adult has swallowed a whole syringe or more, if the product is in-chair strength or unlabelled, or if there is repeated vomiting or stomach or chest pain. Photograph the label; the centre asks for the product and strength. If someone is struggling to breathe or is drowsy, call 000 first. Gel in the eye is a separate problem: flood the eye with cool water for 15 minutes, then ring.
Gel on your lips, gums or tongue
A white patch where gel has sat is a superficial chemical burn. teeth.org.au warns that strong whitening gel touching the lips, gums or tongue can cause burns that often turn into ulcers before they heal. The top layer has been bleached and dehydrated; it stings, peels, and pink tissue returns underneath. In clinical trials of nightguard bleaching, gum irritation and sensitivity resolved within two to three days of stopping treatment.
Take the tray out, wipe the gel off the lip or gum with a clean tissue, and rinse with water. Soft food and a day or two without acidic or spicy food keep it comfortable.
See a dentist if the patch is larger than a fingernail, if it blisters or ulcerates, if the gum pulls away from the tooth, or if anything is still sore after a week. Lumi Dental keeps emergency appointments for exactly that.
Why tray overfill is the usual cause, and how to load one
Most problems start with a tray carrying far more gel than it needs. teeth.org.au notes that your dentist tells you how much gel to use and how to load the trays: a small dot on the front surface of each tooth position, about the size of a grain of rice, no gel along the gum edge, and nothing on the back of the tray. Anything that squeezes out at the edge is wiped away with a clean finger or a dry toothbrush; spit out the saliva that pools, do not swallow it.
A tray made on a scan of your teeth and trimmed in a scallop just short of the gum line holds gel against the enamel and keeps it off the gum. Boil-and-bite chemist trays sit loosely, so gel drifts to the gum and throat. Our article on custom whitening trays explains how they are made.
What to do: a quick guide
| Situation | Do now | See someone if |
|---|---|---|
| Adult swallowed a smear | Spit, rinse, drink water, no vomiting | Nausea or throat pain lasts for hours |
| Adult swallowed a whole syringe or more | Rinse, sip water, ring 13 11 26 with the label | The centre advises it, or vomiting or pain follows |
| Child swallowed gel or chewed a strip | Wipe the mouth, ring 13 11 26 straight away | Always; call 000 if breathing is affected |
| In-chair or unlabelled product swallowed | Rinse, ring 13 11 26 | Always |
| White patch on gum or lip | Remove tray, wipe gel off, rinse, soft food | Blistering, ulcer, or still sore after a week |
| Gel in the eye | Flood with cool water for 15 minutes | Always; eye check if pain or blurring continues |
| Breathing difficulty, drowsiness or swelling | Call 000 | Always |
Children, pets and storing gel
The toxicology reference notes that children are the group most often exposed to dilute peroxide by accident. Keep syringes out of reach, and treat a chewed whitening strip as a swallowed-gel call. The Poisons Information Centre handles people only; for a dog or cat that has chewed a syringe, the Animal Poisons Helpline on 1300 869 738 or your vet is the number. Follow the storage instructions on the box; our article on whether whitening gel expires and how to store it covers that.
How we approach this at Lumi Dental
Every take-home kit at Lumi Dental is issued after an examination by a dentist, with trays made from a 3D intraoral scan and trimmed to keep gel off the gums. We show you how much gel to load, and the hygiene team, our oral health therapists, check fit during whitening maintenance. Our whitening options are Lumi Home, Lumi Refresh and Lumi Radiance, outlined on the teeth whitening page. With in-chair whitening the gums are isolated with a protective barrier before any gel is placed.
Questions patients ask
Is it dangerous to swallow teeth whitening gel?
Not in the amounts a take-home tray holds. Low-strength peroxide breaks down into water and oxygen, and small accidental swallows are described as generally benign. Large amounts, in-chair gel, or any amount in a child are the cases to ring 13 11 26 about.
What does it mean when my gums turn white after whitening?
Gel has sat on the gum long enough to bleach the surface layer, a superficial chemical burn. Wipe it off, rinse, and expect the pink to return over a few days; if it keeps happening, the tray edge or the amount of gel needs adjusting.
How long does a whitening burn on the gums take to heal?
Usually a few days. In nightguard bleaching trials irritation settled within two to three days of stopping, and small ulcers typically heal within a week; anything still sore after that should be looked at. If it is a cold sore or ulcer rather than a burn, our article on whitening with a cold sore or mouth ulcer explains why to wait.
Can I keep whitening if I have burnt my gums?
Pause for a night or two, then restart with less gel and check that the tray edge is not pressing on the gum. In my experience most people need about half the gel they first used; if the same spot burns again, bring the tray in to be adjusted.
What if my child swallowed whitening gel or chewed a strip?
Wipe out the mouth, do not induce vomiting, and ring 13 11 26 straight away with the packaging in your hand. The centre will say whether home observation is enough; call 000 if breathing is affected.
Thinking about whitening safely? Complimentary cosmetic consult in Melrose Park
For whitening planned by a dentist, with custom trays and clear instructions on how much gel to use, the team at Lumi Dental can help. Book a complimentary cosmetic consult at Melrose Central in Melrose Park, or read about teeth whitening at Lumi Dental. Patients visit from Ryde, Parramatta, Ermington and Rydalmere, with on-site parking.
Sources
- StatPearls (NCBI Bookshelf): Hydrogen peroxide toxicity
- NSW Poisons Information Centre: Poisons first aid
- Australian Dental Association (teeth.org.au): Teeth whitening
- Australian Competition and Consumer Commission: ACCC takes action on unsafe teeth-whiteners
About the author
Dr James Tran is a general dentist at Lumi Dental in Melrose Park. He holds a BDent from the University of Sydney and a Graduate Diploma in Oral Implants, and is a Member of the International Congress of Oral Implantologists (MICOI).
This article is general information only and is not a substitute for an examination and individual advice from a registered dental practitioner. Suitability for any treatment varies from person to person.
