How children’s lungs grow

How lungs develop after birth

Your baby’s lungs are ready to breathe as soon as they are born but they continue to develop and grow throughout their life.

Childhood is a really important time for healthy lung development and there are lots of ways you can keep your child’s lungs healthy. The most important things you can do to prevent lung damage are:

At birth

When your child is in the womb, their lungs are filled with fluid. As soon as your child is born they need to start using their lungs to breathe and get their own oxygen from the air.  This is a big change.

Hormones help the lungs to remove the liquid that was in your baby’s lungs.

As your baby takes their first breath, the blood vessels around the lungs get wider and your baby’s blood flows to the lungs to collect oxygen.

0-3 years

Adult lungs have 300 million air sacs. At birth your baby has 50 - 70 million air sacs but they are still not fully developed.

In the first 6 months of your child’s life, they develop a lot of air sacs very quickly.

After 6 months, they develop more slowly.

Your child’s lung volume - the amount of air their lungs can hold - increases a lot during the first two years of their life.

By the time your child is 3, their lungs look like a mini version of adult lungs.

Diagram showing what children's lungs look like at the age of 3

After 3 years

Your child’s lungs get bigger as they grow.  All their airways and air sacs increase in size and volume.

Some studies suggest that your child carries on slowly developing new air sacs throughout their childhood. But more research is needed to say for certain.

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Last medically reviewed: September 2016. Due for review: September 2019

This information uses the best available medical evidence and was produced with the support of people living with lung conditions. Find out how we produce our information. If you’d like to see our references get in touch.