Key points in brief
- An eruption cyst or haematoma is a soft blister on a child's gum, clear or blue-purple, where a tooth is about to come through. It usually goes away by itself once the tooth is through.
- Until then, in most cases watching it is enough if the blister does not hurt, is not growing and does not bother your child when eating or drinking.
- Watch the blister without touching it: do not pierce, cut or squeeze it. Every 2–3 days, photograph it with your phone to see if it is shrinking and if the tooth shows through.
- Show the blister to a dentist if it hurts, bleeds, grows or stays the same for a few weeks. After an injury, or with pus, swelling, fever or refusal to drink, call a doctor the same day.
- The blister lies just under the surface of the gum, so the dentist recognises it by how it looks. It usually does not need a procedure or an X-ray.
Consult your case with an expert and get your treatment plan
Eruption cyst and eruption haematoma: what they are
An eruption cyst is a soft, fluid-filled blister on the gum, exactly where a tooth is about to appear. Before a tooth comes through the gum, its crown - the part you later see in the mouth - sits in a thin sac. As the tooth moves towards the surface, fluid can collect between the crown and this sac and make the gum bulge. Once the crown breaks through the gum, the fluid usually drains away and the blister disappears.
When the fluid is clear, the blister looks like a glassy or slightly bluish bubble. When blood mixes into the fluid, for example after the gum has been bitten during a meal, the blister turns purple or dark blue. Dentists then call it an eruption haematoma, but it is the same thing, and it is dealt with in the same way. Parents often describe it simply as a blue or purple gum, or a blister over the tooth.
The blister can appear over a baby tooth in an infant or a young child. It also appears in older children over a permanent tooth, for example over a front incisor or over a six-year molar. The six-year molar is the first permanent back tooth, and it comes through at around the age of 6.
It is not known exactly why such a blister forms in some children and not in others. We know of no way to prevent it, and the blister itself is not a sign of poor oral hygiene or of mistakes in feeding.
An eruption cyst lies in the gum, above the crown. It is a different condition from a dental cyst in the bone of the upper or lower jaw, which only shows up on an X-ray and usually needs treatment. A dental sinus tract on the gum also looks different. It is a small pimple from which pus may ooze. It appears next to a tooth that has already come through.
In newborns, before the first teeth appear, small whitish bumps are sometimes seen on the gum. They are not related to a tooth coming through and often disappear on their own. Less often, a blue-purple lump appears even though no tooth is coming through yet. Show such a lump to a doctor at your baby's next check-up. If a bump or the lump grows or makes it hard for your baby to suck, have your baby seen by a dentist. A doctor recognises these changes mainly by how they look.
What to watch at home and when to show the blister to a dentist
Until the tooth comes through, it is enough to check five things: how the blister looks, pain, eating and drinking, bleeding, and whether the tooth keeps coming through. The easiest time to do this is once a day, when you clean your child's teeth. If your child is eating, drinking and can be settled, and the blister is not growing, you can calmly keep watching. During this time, do not pierce it or squeeze it. Show the blister to a dentist within the next few days if it is growing, hurts, bleeds, gets bitten at every meal, the gum around it turns red, or nothing has changed after a few weeks.
| What you check | You can keep watching | Book a dental appointment |
|---|---|---|
| Size and colour | the blister is the same size or smaller, clear, bluish or blue-purple | it grows from day to day, or the gum around it turns red |
| Pain | your child is fussy, as when teething, but can be settled | cries when the gum is touched or when biting |
| Eating and drinking | eats and drinks as usual, may want to chew on things more | avoids food because it hurts, or bites the blister at every meal |
| Bleeding | the blister does not bleed | you see blood on the spoon, the dummy or the gum |
| Time and the tooth | from week to week the blister gets smaller, or the crown is already showing through the gum | after a few weeks nothing has changed and the tooth still cannot be seen |
Every 2–3 days, take a photo of the blister with your phone. A few such photos - ideally taken at the same time of day and in similar light - will show the dentist whether the blister is shrinking, growing or staying the same.
Through a clear blister you can often see the white crown of the tooth, which gets closer to the surface over time. With a blue-purple eruption haematoma the crown usually cannot be seen, so in that case it is better to compare the size of the blister from one photo to the next.
With some symptoms, you should not wait a few days. Call the practice the same day if:
- pus or a yellowish fluid is oozing from the blister,
- the gum around the blister has swollen, or there is swelling of the cheek, the lip or the area under the jaw,
- your child has a fever,
- your child will not drink or is noticeably weak,
- a blue-purple blister appeared after a knock to the face.
Pus and swelling usually mean an infection. It may involve the cyst itself, but also a neighbouring tooth with decay, as with a tooth abscess. In a young child, a fever and refusing to drink also need to be assessed by a paediatrician, even if a tooth is coming through at the same time.
If the swelling makes it hard for your child to breathe or swallow, call 112. If the practice is closed and the swelling is getting worse, your child has a fever, will not drink or is noticeably weak, use out-of-hours medical care or an emergency dental service. Pain, a growing blister or biting it while eating does not need such urgency and can usually wait until the practice is open.
How to look after your child until the tooth comes through
Clean the teeth and gums as usual with a soft toothbrush, and move it gently around the blister, without pressing. You can give a baby a clean teething ring cooled in the fridge to chew on. Do not freeze it, because a very cold, hard teething ring can irritate the gum.
Minor discomfort while baby teeth are coming through, most often wanting to chew and irritability, happens in most young children. On its own, it is not a sign that something is wrong with the blister.
Do not use numbing gels on a young child's gums without a doctor's advice. If pain makes it hard for your child to sleep or eat, decide on a painkiller and its dose together with a paediatrician or a dentist.
In an older child, a blister over a six-year molar sometimes gets bitten. It is then more likely to hurt during meals and to bleed. Soft food cut into small pieces helps. If the blister hurts, bleeds or gets bitten at every meal, show it to a dentist.
If a blister has appeared over one tooth, one may also appear over the next tooth, and sometimes over several teeth at once, for example over the neighbouring incisor. You then do the same: watch the blister, take photos, and see a dentist if it starts to hurt, grow or bleed.
How the dentist may help
An eruption cyst or eruption haematoma usually does not need treatment. The dentist most often suggests watching it and books a check-up in a few weeks, or asks you to call if any of the symptoms described above appear. If the blister hurts, is infected, gets in the way of eating, or the tooth still does not come through as time passes, the dentist may uncover the tooth.
If the tooth needs to be uncovered, the dentist numbs the area with a local anaesthetic and cuts through the thin layer of gum over the crown. The fluid drains, the crown becomes visible and the tooth can then carry on coming through on its own. If there is an infection, the dentist also judges whether a medicine, such as an antibiotic, is needed as well as uncovering the tooth.
The dentist usually takes a biopsy, that is, a small piece of tissue to be examined under a microscope, only if the blister looks unusual. In young children there are rare lumps with a similar blue-purple appearance, and the dentist deals with these differently.
A visit to a paediatric dentistry practice is usually enough for the assessment, and for a baby it is sometimes their first dental visit. Bring the photos on your phone to the appointment, and say whether your child has recently had a knock, a fever or any medicines. Once the six-year molar has come through, ask at a check-up about fissure sealants in children.
Why you must not pierce the blister yourself
The blister looks easy to empty, but piercing it at home does more harm than good. Do not do any of these things at home:
- do not pierce the blister with a needle or a pin,
- do not cut it with a razor blade, scissors or a fingernail,
- do not squeeze it or press on it with a finger,
- do not put alcohol or skin disinfectants on it.
A needle or a fingernail can carry bacteria into a fresh wound over a tooth that is still coming through. An infected blister hurts and often needs a visit that calm watching could have avoided. Piercing also does not make the tooth come through any faster, because the fluid usually collects again until the crown breaks through the gum. The blue-purple colour does not mean there is pus inside that needs to be let out. It is blood mixed into the fluid, and it does not need to be removed. Explain to an older child that they should not touch the blister with their fingers or try to bite through it.
If the blister bursts on its own, for example while your child is eating, a little blood-stained fluid usually comes out. Place a clean piece of gauze on the gum and hold it there gently, and show the gum to a dentist within the next few days. If the bleeding does not stop even with the gauze, or pus appears, call the practice the same day.
What to do when a blister appears over your child's tooth
Until the tooth breaks through the gum, compare the photos, check that your child is eating and drinking, and do not touch the blister. A visit in the next few days is needed for pain, bleeding, a growing blister or no change for a few weeks. If there is pus, swelling around the blister or of the face, a fever or refusal to drink, or after an injury, call the same day. Usually, an eruption haematoma and a clear eruption cyst go away by themselves once the tooth is through.
Frequently asked questions
Is an eruption cyst dangerous?
An eruption cyst is usually not dangerous. It is a fluid-filled blister in the gum over a tooth that is coming through. Most often it disappears when the tooth breaks through the gum. It is not a tumour, and on its own it does not damage the tooth. Sometimes pain, biting or an infection causes trouble. Rarely, it turns out to be a different condition that only looks similar.
How long can a blue-purple blister over a tooth last?
It usually lasts until the crown of the tooth breaks through the gum. In one child this takes a few days, in another a few weeks, because teeth come through at different speeds. What matters more than the number of days is whether the blister gets smaller from one photo to the next. If nothing has changed after a few weeks, show it to a dentist.
Can a child with a blister over a tooth eat normally?
Yes, in most cases a child can eat and drink as usual, including a breastfed or bottle-fed baby. If the blister hurts when your child bites, show it to a dentist within the next few days, and until then give soft food that is not too hot. If a young child refuses to drink, that is a reason to call a doctor the same day.
Does an eruption cyst need an X-ray?
Usually not, because the dentist recognises it by how it looks. In a child, an X-ray is taken only after an examination, and only if its result could change the decision about treatment. This is sometimes the case when the blister looks unusual, is growing, or the tooth is taking a long time to come through. The X-ray then shows whether there is a cyst or another obstacle in the bone under the gum that is holding the tooth back.
Can a blue or purple gum in a child be caused by a knock?
Yes. A blue-purple haematoma can appear on the gum after a fall or a knock to the mouth, including where a tooth is coming through. If your child has fallen or hit their mouth and you then notice a blue or purple gum, call the practice the same day. An injury can damage baby teeth and the developing permanent teeth, so a dentist should check it.
Should a blister over a tooth be seen by a paediatrician or a dentist?
A blister over an erupting tooth on its own is best shown to a dentist, because the dentist assesses the gum and the tooth. If your child has a fever, will not drink or is noticeably weak, also call a paediatrician the same day. These symptoms need a paediatrician's assessment, even if a tooth is coming through at the same time.
What does the gum look like in the first few days after the blister is cut open?
After the cut, you can usually see part of the crown of the tooth, surrounded by a reddened edge of gum. In the first 24 hours there may be a little bleeding when your child eats, and the gum may be tender for a few days. Give soft food and brush the teeth gently. If swelling, pus or a fever appears, call the practice the same day.
Read more:
- Paediatric dentist in Warsaw Wola
- Paediatric dentistry: How to prepare your child for their first dental visit — a guide for parents
- Fissure Sealants in Children — When, How Often, and Whether They Really Protect Against Caries
- Tooth abscess — does a tooth with an abscess always have to be removed?
- Comprehensive dental review: What does it contain and why is it crucial for health?
Content and liability disclaimer
This article is informational and educational in nature and does not constitute medical advice, a diagnosis or a therapeutic recommendation — it does not replace a consultation with a specialist. If you are experiencing symptoms, have doubts or are facing a decision about treatment, consult a dentist. The methods described and the data cited are general in nature. The results of scientific studies relate to populations, not to an individual patient. The course and outcome of therapy depend on the individual clinical situation and may vary between patients. No information contained in this article constitutes a guarantee of result. The content has been prepared with due care, based on publicly available medical knowledge and the scientific publications indicated in the Sources section. We do not advise taking or refraining from any health-related action solely on the basis of the content of this article, without prior consultation with a doctor.
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