When Do Babies Start Breathing Through Their Mouth?

Last reviewed: November 6, 2026. Checked against current guidance from the American Academy of Pediatrics (HealthyChildren.org), Seattle Children’s and Cleveland Clinic.

Breathing is one of the first and most essential functions a newborn performs. But did you know that newborns primarily breathe through their noses?

If you’ve ever wondered, “When do babies start breathing through their mouth?”, you’re not alone.

This blog post breaks down everything you need to know—from how infant breathing works to when and why babies transition to mouth breathing.

We’ll also cover warning signs, causes, and when to see a doctor.

Why Do Newborns Breathe Through Their Nose?

At birth, babies are considered obligate nasal breathers. This means they instinctively breathe through their noses, not their mouths.

It’s a design feature of newborn anatomy that serves a few important purposes:

• Allows babies to breathe while feeding

• Helps filter, warm, and humidify the air

• Supports a healthy sense of smell for bonding and feeding

This built-in mechanism keeps babies breathing efficiently even when they’re nursing or lying on their backs.

So, When Do Babies Start Breathing Through Their Mouth?

The ability to mouth-breathe typically develops between 3 to 6 months of age.

Before this, the soft palate and epiglottis are positioned in a way that makes mouth breathing inefficient and uncomfortable.

That said, in emergency situations—like if the nose is completely blocked—a baby can breathe through the mouth, even from birth.

However, because this doesn’t come naturally, some babies struggle with it, which is why nasal congestion in newborns can be serious.

Quick Tip: Always monitor your baby during colds. If they’re having trouble breathing and feeding, consult your pediatrician.

Is Mouth Breathing Normal for Babies?

Occasional mouth breathing can be normal, especially during:

• Colds

• Crying episodes

But persistent or regular mouth breathing is not typical and may signal a problem.

Signs Your Baby Is Breathing Through Their Mouth

Here are some telltale signs your baby may be breathing through their mouth:

• Open mouth while sleeping

• Dry mouth or lips

• Snoring or noisy breathing

• Difficulty feeding

• Frequent nasal congestion

• Restless sleep or irritability

If these symptoms persist for more than a few days, it’s time to look deeper.

Common Causes of Mouth Breathing in Babies

There are several possible reasons why your little one might be breathing through their mouth:

1. Nasal Congestion

The most common reason. A stuffy nose from a cold, allergies, or dry air can force a baby to breathe through their mouth.

2. Enlarged Adenoids or Tonsils

These lymphatic tissues can block nasal airflow, especially if they’re enlarged.

3. Deviated Septum or Nasal Blockage

Structural abnormalities can cause chronic nasal obstruction.

4. Sleep Apnea

Though rare in infants, sleep apnea can cause interrupted breathing patterns and mouth breathing at night.

5. Habitual Behavior

Older infants might develop a habit of mouth breathing even after congestion has cleared.

How to Encourage Nasal Breathing

If your baby is mouth breathing due to congestion or habit, here are some helpful steps:

1. Use Saline Drops

A few drops in each nostril can loosen mucus and help clear the nasal passages. For babies, 1 to 2 drops per nostril is enough. Don’t give over-the-counter cough and cold medicines to children under 4.

2. Try a Nasal Aspirator

Use a bulb syringe or electric aspirator to gently remove mucus. A bulb syringe works best for babies under 6 months.

3. Use a Humidifier

Adding moisture to the air can prevent dryness and reduce irritation. Place it near your baby but out of reach, and clean it often to stop mold and bacteria from growing.

4. Keep Sleep Flat and on the Back

Don’t raise the head of the crib or mattress, and don’t use pillows or wedges. The American Academy of Pediatrics advises against propping up a congested baby, because it can bend the neck and narrow the airway. Always place your baby on their back on a firm, flat surface. Read more in our guide to the safest sleeping position for a baby with a stuffy nose.

5. Keep the Air Clean

Avoid smoke, dust, or strong scents that may irritate your baby’s sensitive nasal passages.

When to Call the Pediatrician

Persistent mouth breathing should not be ignored. Contact your doctor if:

• Mouth breathing lasts more than a few days

• Your baby struggles to feed or gain weight

• You notice snoring or gasping during sleep

• There’s visible discomfort during breathing

• Your baby is breathing much faster than normal

• Your baby seems lethargic or excessively irritable

• Your baby is under 3 months and has a rectal temperature of 100.4°F (38°C) or higher. Call right away.

Call 911 if your baby is struggling with each breath, their lips or face look blue, or they stop breathing. Go to the ER if their ribs pull in with each breath.

Your pediatrician may refer you to a specialist such as an ENT (Ear, Nose & Throat doctor) to rule out structural issues or sleep disorders.

Can Mouth Breathing Affect Development?

Chronic mouth breathing isn’t just a breathing issue—it can also impact development:

• Facial Structure: Long-term mouth breathing in children can change the shape of the face and jaw and how the teeth line up

• Behavior: Poor sleep from a blocked airway can make children irritable and restless

• Sleep Quality: Poor sleep affects mood, behavior, and cognitive development

Early detection and intervention are key to preventing long-term problems.

Summary: Key Takeaways

Final Thoughts

Babies are natural nose-breathers, and for good reason—it’s safer, healthier, and more efficient. While the ability to breathe through the mouth develops as they grow, persistent mouth breathing could signal something more serious.

Keep an eye on your baby’s breathing habits, especially during colds or if sleep becomes disrupted. When in doubt, don’t hesitate to reach out to your pediatrician.

This article is for general information and isn’t a substitute for medical advice. Always contact your pediatrician with questions about your baby’s health.