The most common cause: fluid trapped behind the eardrum after a cold or respiratory infection
Most ear infections in babies happen because the Eustachian tube—a small passage that drains fluid from the middle ear—gets blocked. When your baby has a cold, flu, or other respiratory infection, the tissue inside that tube swells up. Fluid that normally drains out gets stuck instead, and bacteria or viruses grow in that trapped fluid.
This is why ear infections often come a week or two after you notice your baby has been congested or has had a runny nose. The infection itself is not in the outer ear you can see; it is in the middle ear, behind the eardrum. That is why your baby cannot blow their nose or clear it the way an older child can.
Babies are more prone to this than older children because their Eustachian tubes are shorter, narrower, and more horizontal. Fluid does not drain as easily. By around age 3, the tubes lengthen and angle downward, which is why ear infections become less common as children get older.
Key Takeaways
- Ear infections in babies usually start when a cold or respiratory virus causes the Eustachian tube to swell and trap fluid behind the eardrum.
- Babies' Eustachian tubes are shorter and more horizontal than older children's, making drainage harder and infections more likely.
- Secondhand smoke, bottle feeding while lying flat, and time spent in group childcare all increase the risk of ear infections.
- Signs include pulling at the ear, fever, fussiness, or fluid draining from the ear, though some babies show no symptoms at all.
- Most ear infections clear on their own within two to three weeks, though a doctor should examine your baby to rule out other causes.
Why some babies get more ear infections than others
Certain situations make ear infections more likely. Babies who spend time in group childcare are exposed to more colds and respiratory viruses, which means more chances for fluid to get trapped. Babies who are bottle-fed while lying flat are at higher risk because fluid can flow into the Eustachian tube more easily from that position; breastfeeding and feeding in an upright position lower the risk.
Secondhand smoke irritates the lining of the Eustachian tube and makes swelling worse. Babies with cleft palate or Down syndrome have structural differences that affect how the tube works. Seasonal changes matter too—ear infections peak in fall and winter when colds are more common, and they are less common in summer.
Allergies can also play a role. If your baby's nasal passages are inflamed from allergies, the Eustachian tube is more likely to swell and block. However, true allergies are rare in very young babies; what looks like allergies is usually a cold or other infection.
Bacterial versus viral infections and why it matters
The fluid trapped in the middle ear can be infected by bacteria or by a virus. Viral infections—from colds, flu, or other respiratory viruses—usually clear on their own as your baby's immune system fights them off. Bacterial infections may need antibiotics, though many clear without them too.
A doctor cannot tell which type of infection your baby has just by looking in the ear. They use an otoscope to see whether the eardrum is bulging (which suggests pressure from fluid) and may use a tool called a tympanometer to measure whether fluid is present. Even with these tools, determining whether bacteria or a virus is responsible requires a sample of the fluid itself, which doctors rarely take unless the infection is severe or keeps coming back.
This is why doctors often watch and wait rather than prescribe antibiotics immediately. If your baby is under 6 months old, has a high fever, or seems very ill, antibiotics are more likely to be recommended right away. For older babies with mild symptoms, doctors may suggest pain relief and observation for a few days to see whether the infection clears on its own.
Fluid in the ear that lingers after infection clears
After an ear infection gets better, fluid sometimes stays in the middle ear for weeks or even months. This is called otitis media with effusion, or fluid in the ear. Your baby may not have pain or fever anymore, but the fluid is still there, and it can muffle sound.
Most of the time this fluid drains on its own within three months. If it stays longer than that, or if it is in both ears and affecting your baby's hearing during a critical time for language development, a doctor may recommend further evaluation. Hearing matters for speech development, so if your baby is between 6 months and 3 years old and has had persistent fluid, your doctor may refer you to an audiologist to check whether hearing is affected.
What you might notice: signs that point to an ear infection
Babies cannot tell you their ear hurts, so you have to watch for signs. The most common is pulling or tugging at the affected ear, especially during or after a feeding or when your baby is lying down. Fever is common but not always present—some babies have ear infections with no fever at all. Your baby may be fussier than usual, sleep poorly, or lose interest in eating.
If you see fluid or pus draining from the ear, that means the pressure behind the eardrum has ruptured the eardrum. This looks alarming but is actually a sign that pressure is being released. The eardrum usually heals on its own. Vomiting or diarrhea sometimes happen alongside an ear infection, though these are not specific to the ear and could point to other causes.
Some babies have no symptoms at all and the infection is found only when a doctor examines them for another reason. This is why doctors often check the ears during routine visits, especially if your baby has recently had a cold.
How colds and other infections lead to ear infections
The path from a cold to an ear infection is straightforward. Your baby catches a respiratory virus—usually from another child, a family member, or contaminated surfaces. The virus inflames the lining of the nose, throat, and the passages that connect to the ears. Mucus production increases. The Eustachian tube, which is already narrow in babies, swells from the inflammation and closes off.
Fluid that would normally drain into the throat gets trapped instead. Within days, bacteria that live normally in the nose and throat move into that trapped fluid and multiply. The immune system responds with inflammation, which increases pressure behind the eardrum. That pressure is what causes pain.
This is why preventing colds reduces ear infections: fewer colds mean fewer chances for the Eustachian tube to swell. Hand washing, keeping your baby away from sick people when possible, and avoiding secondhand smoke all reduce cold risk. Breastfeeding also provides antibodies that help fight infections.
When to see a doctor and what to expect
See a doctor if your baby has signs of an ear infection: fever, ear pulling, fussiness, or drainage from the ear. You should also see a doctor if your baby has had a cold for more than 10 days and is not improving, because that can signal a secondary ear infection. If your baby is under 6 months old and has any fever, contact your doctor regardless of other symptoms.
At the visit, the doctor will look in your baby's ears with an otoscope and may check for fluid using a tympanometer. They will also listen to your baby's lungs and check for other signs of infection. If your baby is in pain, ask about pain relief options—acetaminophen or ibuprofen (if your baby is old enough) can help while you wait to see whether the infection clears on its own.
If antibiotics are prescribed, give them exactly as directed, even if your baby seems better after a few days. If no antibiotics are prescribed and your baby is not improving after three days, or if symptoms get worse, call your doctor again. Some infections need antibiotics even if they were not prescribed initially.
Frequently Asked Questions
Can teething cause ear infections?
Teething does not cause ear infections, but babies who are teething often drool more and may have swollen gums that make them uncomfortable. Parents sometimes mistake teething pain or discomfort for an ear infection. If your baby is pulling at their ear and has other signs like fever or fussiness, see a doctor to rule out infection rather than assuming it is teething.
Will my baby's ear infection come back?
Some babies have one ear infection and never have another. Others have several, especially if they are in group childcare or have frequent colds. Recurrent infections (three or more in six months) may warrant further evaluation by an ear, nose, and throat specialist, but most babies outgrow the tendency to get them as their Eustachian tubes mature.
Is it safe to let an ear infection go untreated?
Most ear infections clear on their own, but you should still have a doctor examine your baby to confirm it is an ear infection and not something else. Untreated infections can occasionally lead to complications like a ruptured eardrum or spread to nearby tissues, though this is rare. A doctor can help you decide whether to treat with antibiotics or watch and wait.
Does swimming or water in the ear cause ear infections?
Water in the outer ear canal does not cause middle ear infections. However, if your baby has a hole in the eardrum from a previous infection, water can enter the middle ear and cause problems. If your baby has had a ruptured eardrum, ask your doctor whether you need to protect the ear during baths or swimming.
Can I prevent ear infections?
You cannot prevent all ear infections, but you can reduce the risk. Breastfeed if possible, feed your baby upright rather than lying flat, avoid secondhand smoke, keep your baby away from sick people when you can, and practice good hand washing. Keeping up with vaccinations also helps prevent some of the infections that lead to ear problems.