An eruption cyst is a fluid-filled bump that forms on the gum just before a tooth breaks through. It appears as a bluish, clear, or purplish dome sitting right over the spot where a new tooth is pushing up. These cysts are harmless in the vast majority of cases and resolve on their own once the tooth comes in.
If you’ve noticed a strange-looking bump on your child’s gums, this is most likely what you’re looking at. Here’s what causes it, what to expect, and when it might need attention.
How an Eruption Cyst Forms
As a tooth moves upward through the jawbone toward the surface of the gum, it’s surrounded by a thin sac called the dental follicle. Normally, this sac stays tightly attached to the tooth as it pushes through. Sometimes, though, the follicle separates slightly from the tooth’s surface, and the small space between them fills with fluid or blood. That pocket of fluid creates a visible bump on the gum tissue, right over the incoming tooth.
Because the cyst sits in the soft tissue of the gum rather than deeper in the bone, it’s considered a soft-tissue version of a dentigerous cyst (a similar fluid-filled sac that forms around unerupted teeth still embedded in the jaw). The key difference is location: eruption cysts are superficial, sitting at or near the gum surface where you can see and feel them.
What It Looks Like
Eruption cysts have a distinctive appearance. They look like a soft, dome-shaped swelling on the ridge of the gum, directly over where you’d expect a tooth to come in. The bump is usually soft to the touch and slightly squishy. Its color depends on what’s inside.
- Clear or translucent: When the cyst contains only fluid, it may look like a small, clear blister.
- Bluish or purple: A blue, purple, or blue-black color means blood has mixed with the fluid inside the cyst. This darker version is sometimes called an eruption hematoma. It looks more alarming but is equally harmless.
- Yellowish: In some cases, particularly in very young infants, the cyst may appear yellowish.
The size varies. Some are barely noticeable, while others can measure over 2 centimeters across. The overlying gum tissue is typically smooth with no ulceration or open sores.
Who Gets Them and Which Teeth Are Involved
Eruption cysts show up most often in children under 10. A study of 66 cases found the average age was about 5.4 years, though they can appear as early as the first few months of life in newborns whose baby teeth are coming in. They occur with both baby teeth and permanent teeth, with permanent teeth slightly more common (about 59% of cases versus 41% for primary teeth).
Not all teeth are equally likely to develop them. Among baby teeth, the upper first molars are the most common site, accounting for nearly two-thirds of primary tooth cases. For permanent teeth, the upper central incisors (the two front teeth) are the most frequently affected, involved in more than half of permanent tooth cases. Over half of all eruption cysts appear in the upper jaw rather than the lower.
Children can develop a single cyst or multiple cysts at the same time, on one side or both sides of the mouth.
How Long They Last
Most eruption cysts resolve on their own as the tooth pushes through and breaks the surface of the gum. The timeline varies, but documented cases give a reasonable sense of what to expect.
In newborns, where the process tends to be slower, cysts have been observed shrinking noticeably within about a month, with complete resolution by two to four months as the teeth fully emerge. One case showed the cyst nearly gone within 45 days, with full regression by 60 days. In older children with permanent teeth coming in, the process can be faster since the tooth is already close to the surface.
The typical pattern is gradual: the cyst slowly decreases in size, its color shifts back toward normal gum tissue, and then the tooth pokes through. Once the tooth breaks the surface, the remaining cyst tissue simply becomes part of the normal gum around the new tooth.
When Treatment Is Needed
The standard approach is observation. Because eruption cysts almost always resolve once the tooth erupts, most dentists recommend simply watching and waiting. No medication or intervention is necessary in routine cases.
Occasionally, a dentist may recommend a minor procedure if the cyst is unusually large, appears infected, is causing significant pain or difficulty eating, or if the tooth seems unable to break through on its own after an extended period. The procedure involves making a small opening in the top of the cyst to release the fluid and expose the tooth underneath, allowing it to finish erupting. This is straightforward and heals quickly.
What Parents Can Do at Home
If your child has an eruption cyst, the most important thing is to leave it alone. Don’t try to pop or squeeze it. Letting your child chew on a clean, cold teething ring or washcloth can help with any soreness, just as it would during normal teething. Keeping the area clean with gentle brushing around (not on) the cyst helps prevent irritation.
Watch for signs that something more is going on: increasing redness or swelling that spreads beyond the cyst itself, pus, fever, or significant pain that interferes with eating or sleeping. These could suggest infection rather than a simple eruption cyst and are worth a visit to the dentist. But in the vast majority of cases, the bump will quietly disappear as the new tooth arrives.