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Human Milk Oligosaccharides (HMOs) & Infant Immune Health

0-4 months
Article

Human Milk Oligosaccharides (HMOs) & Infant Immune Health

Nov 26, 2025
6 mins

Explore the role of Human Milk Oligosaccharides (HMOs) in breast milk and how they support infant immunity and promote a healthy gut.

When it comes to feeding your baby, nothing beats breast milk.  Breast milk provides the best start in life for babies. It has so many important nutrients and other special components in a combination that no other food provides. 

 

One of those unique components is Human Milk Oligosaccharides (HMOs).  HMOs in breast milk play a vital role in the immune system development of babies. They nourish beneficial gut bacteria, and support a healthy digestive system to help protect against harmful gut bacteria. By supporting a healthy digestive tract, HMOs in breast milk contribute to the overall health and well-being of infants.

Understanding Human Milk Oligosaccharides (HMOs)

Human Milk Oligosaccharides in breast milk are unique complex carbohydrates known as natural prebiotics. HMOs make up a significant part of human milk, being the third largest solid component after lactose and fat.

Over 200 HMOs have been identified so far, with a wide diversity in breastfeeding mums.  The most abundant HMO is Oligosaccharide 2’-Fucosyllactose (2’-FL) with approximately 80% of women worldwide producing 2’-Fucosyllactose in their breast milk.

These HMO “prebiotics” are not to be confused with ‘probiotics’ which are beneficial bacteria that can be found in some foods and supplements – read more about ‘probiotics’ here.

HMOs and infant gut health

HMOs in breast milk support infant gut health by providing food for your baby’s beneficial gut bacteria, making them a natural ‘baby prebiotic’.

There are many different types of beneficial gut bacteria, with Bifidobacteria and Lactobacillus being the more common types. Breastfed babies gut bacteria is made up mostly of Bifidobacteria and Human Milk Oligosaccharides have a big role to play in that, as they are an excellent source of food for these friendly bacteria.

Supporting a healthy digestive system by feeding the good bacteria, where approximately 80% of our immune cells live, is a way HMOs support the baby immune system. 

HMOs and the newborn immune system

From the moment your little one is born, early exposure to different things triggers the newborn immune system to start defending for itself. In Australia, most babies start on breast milk, which is fantastic as breast milk not only nourishes your baby, it also contains immune cells, growth factors and special bioactive components such as HMOs that all support a newborn immune system.

Infancy is a critical period for immune system development and nurturing early defence mechanisms is key. HMOs in breast milk have been shown to support the developing immune system in these four ways:

What is the gut barrier and how do HMOs in breastmilk help it function?

The gut barrier is a crucial part of your baby’s digestive system. This protective barrier or layer that runs all along the gut and intestines is one of the main defence mechanisms for our body. When strong and functioning, it’s job is to keep harmful substances, pathogens, and toxins from entering the bloodstream while letting all the good stuff, like nutrients in to be absorbed. This barrier is essential for a growing baby as it supports the absorption of nutrients, the development of a healthy immune system, and overall well-being. Human Milk Oligosaccharides (HMOs) play an important role in enhancing the function of the gut barrier. As food for the good bacteria in your baby’s tummy, HMOs promote the growth of beneficial gut bacteria which in turn strengthens the gut lining. By strengthening and reinforcing the gut lining, HMOs gently support immune responses by reducing the risk of infections and inflammation. 

Related FAQ's

What are oligosaccharides?

Parenting FAQs

Oligosaccharides are short chains of carbohydrates found in various foods, also known as prebiotics. They are mostly not digested by our bodies but serve as food for beneficial bacteria in our gut, such as Bifidobacteria. These bacteria help support the digestive tract and the immune system. Breastfeeding provides unique human milk oligosaccharides, such as 2 Fucosyllactose which can contribute to a healthy gut and overall well-being.

What is in human milk?

Parenting FAQs

Human milk, or breast milk, is the natural milk produced by a lactating woman. It is a complete and balanced source of nutrition for infants, containing essential nutrients, antibodies, and other bioactive ingredients such as Human Milk Oligosaccharides that support their growth and development. Breast milk provides numerous health benefits and is recommended as the best source of nutrition for babies.

When do newborns immune system develop?

Parenting FAQs

The immune system of newborns begins to develop during pregnancy and continues to strengthen after birth. However, it takes time for their immune system to fully mature. During this period, it is important to provide your baby with a healthy environment and proper nutrition to support their immune system development.

Is Bifidobacteria good or bad?

Parenting FAQs

Bifidobacteria are beneficial bacteria that naturally live in our gut. They play a crucial role in maintaining a healthy digestive system and supporting overall well-being. Bifidobacteria help guard the gut against harmful bacteria getting in. Therefore, they are considered good bacteria that contribute to our health.

When does a baby’s gut mature?

Parenting FAQs

A baby's gut begins to mature during pregnancy, but it continues to develop after birth as the intestines continue to grow throughout childhood until they stop growing. During this time, the gut undergoes changes that allow for the proper digestion and absorption of nutrients, supporting a child's overall health and well-being.

What is 2' Fucosyllactose?

Parenting FAQs

2 Fucosyllactose (2’-FL) is a Human Milk Oligosaccharide (HMO) which is a short chain of special sugar molecules, found in human breast milk. It is a unique carbohydrate that provides important benefits to infants. 2 Fucosyllactose acts as a prebiotic, feeding beneficial bacteria in the baby's gut and supporting a healthy digestive system. By supporting a healthy digestive tract it also helps strengthen the baby's immune system, helping overall growth and development.

What are the nutritional requirements for infants?

Parenting FAQs

The nutritional requirements for infants include macronutrients and essential vitamins and minerals that support their growth and development. Breast milk provides all the essential nutrients such as proteins, carbohydrates, fats, vitamins, and minerals for an infant until around 6 months of age. At around 6 months of age solid foods can be introduced to help meet increased nutritional requirements. If a baby is not breastfed, an infant formula is the only suitable substitute.