What Age Is a Child's Immune System Fully Developed?


The immune system protects us from illnesses and germs. It consists of cells, proteins, tissues and organs that work together to fight these invaders. As we get older, our immune system develops and becomes stronger.

How Do You Know If Your Child Has A Weak Immune System?

Some children have a weak immune system. This can be from medications or chronic diseases. Oftentimes a child with a weak immune system:

  • Has cancer
  • Has had organ transplants
  • Has HIV or AIDS
  • Was born with abnormalities of the immune system
  • Has diseases that require the use of certain medications like corticosteroids

How Long Does It Take To Build A Child’s Immune System?

Parents can start building children’s immune systems from the moment they are born, but how long does it take to build a child’s immune system? And they can encourage good habits as the child grows to continue boosting the immune system. Here are some steps to consider baby immune system development:

Breastfeed If Possible

If you can breastfeed your child, aim for at least six months. It can help reduce risk of infections and allergies in babies.


Follow the pediatrician’s advice about children’s immunization schedule. Some children with weakened immune systems may need a more specialized schedule.

Sleep Schedule

It’s important for growing children to get enough sleep. And that requirement will vary as children get older. Typically:

  • 3-5 year olds need 10-13 hours
  • 6-13 year olds need 9-11 hours
  • 14-17 year olds need 8-10 hours

Wash Hands

Up to 80% of infections are transmitted by touch so it’s important to teach children when they are young how important it is to wash their hands especially after sneezing, coughing or going to the bathroom.

Eat Healthy

Sometimes it isn’t easy to get kids to eat healthy, especially if you have a picky eater, but work with your child to eat fruits, vegetables and whole grains while limiting processed foods. Getting enough vitamins can strengthen the immune system

At What Age Does A Child’s Immune System Fully Develop?

Children’s immune systems continue to develop after they are born, but at what age is the immune system fully developed? They are at risk of illnesses including viruses and bacteria as their immune system develops and immunological memory kicks in to fight off invaders. Typically immune systems become fully developed around age 7-8 (1).

Does A Child Getting Sick Build Their Immune System?

There is some truth to the idea that children who are exposed to colds and viruses earlier in life will develop a stronger immune system. They are also less likely to become sick later on. This is because immunity is immunity so there is some correlation with age and the immune system.

So as much as parents don’t want to see their child sick, it could actually help them. This is because their body will recognize the illness and fight it off, continuing to build immunity.

It’s important to remember there are many different viruses. For example, there are actually hundreds of different cold viruses so if a child gets immunity to one, there are still hundreds more out there. This is one reason why good hygiene is so important.

When Does The Baby Immune System Get Stronger?

Right after a baby is born, their immune system kicks into high gear. Researchers found that it is actually very dynamic early on. They analyzed 100 premature and full-term babies for the first few weeks of life. All followed the same similar changes with their immune systems responding with the same sequence of changes.

Researchers now want to analyze the immune system as babies get older to see how the immune system adapts to the external environment. Their goal is to follow them into childhood to see who develops certain illnesses including allergies and asthma to have a better understanding of what changes.

Are Children’s Immune Systems Better Than Adults?

At what age is the immune system strongest? Children’s immune systems compared to adults are not as efficient. Children are more likely to get viral infections and take more time to recover from them for a number of reasons mostly because they are continuing to grow and develop.

As children’s systems develop, not just their immune system, but all other systems as well including their nervous, digestive and reproductive systems, they are more vulnerable.  

When a child has been exposed to an illness and recovered from it, their body builds immunity. So if a child or adult comes in contact with it again, their immunological memory will kick in and know this is an invader that needs to be fought. Adults have been exposed to more viruses, illnesses and bacteria so their immunological memory is stronger.

How Can I Boost My Child’s Immune System?

Besides just washing hands, making sure your child is receiving proper immunizations and getting enough sleep, there are other ways to boost the immune system. There are some vitamins that children should consume for immunity support.

Vitamin C

A huge immunity booster. But if the body doesn’t have enough, it can make people more prone to getting sick. It’s important to get enough each day because the body doesn’t store it. The good news is that it is found in a lot of different foods including:

  • Oranges
  • Grapefruit
  • Tangerines
  • Strawberries
  • Bell peppers
  • Spinach
  • Kale
  • Broccoli 

Vitamin B6

This vitamin can support biochemical reactions in the immune system. Chicken, salmon and tuna are rich in B6. It can also be found in green vegetables and chickpeas. 

Vitamin E

Nuts, seeds and spinach are rich in vitamin E, which is a powerful antioxidant that helps the body fight off infections.

Eating healthy foods in general can help boost the immune system. A strong immune system can help fight off any illnesses right away. You can’t just expect to give your child some orange juice when they get the sniffles and hope it will have the same effect. Fill their plates with colorful fruits and vegetables to make meals interesting to look at and super healthy.

Supplements That Can Help

The immune system contains cells so it’s important to make sure cells are always healthy. Spermidine is a supplement that can activate the body's cellular renewal process called autophagy. This is the body’s way of getting rid of old, damaged cell parts so new and healthy ones can be formed. When cells are new and healthy, they operate at the highest efficiency possible providing strength to the immune system


  1. Evolution of the immune system in humans from infancy to old age

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  • Don Moxley - Director of Applied Science

    Don Moxley is the Director of Applied Science at Longevity Labs. Moxley draws upon his career as an athlete, a sports scientist, and an instructor to lead and educate on the science of autophagy and longevity.