The immune system is a complex network of cells and cell components acting together to protect a baby from diseases caused by bacteria, viruses and other foreign substances.

There are several types of immunity that a baby acquires, and these work together in order to protect him from illness.

Passive immunity is acquired while the baby is still in its mother's womb. Antibodies pass from the mother's bloodstream directly to the baby. This gives the baby temporary immunity for about six months.

Adaptive immunity, also known as active immunity, develops throughout our lives as we grow and become exposed to diseases or when we are immunised against them through vaccination.

It is this type of immunity which detects and eliminates bacteria or viruses that make their way into the body because they can reproduce.

The third type of immunity is called innate immunity and consists of the external barriers of the body, like the skin, mucous membranes of the throat and the gastrointestinal tract.

Innate immunity in the digestive tract counts for two thirds of the body's immune system and is built through the introduction of healthy bacteria that lay the foundation for a strong immune system.

These healthy bacteria can reduce allergies and infections by creating a strong gut barrier against infectious organisms and allergens.

They also promote the development of the Gut Associated Lymphoid Tissue (Galt), which produces and stores immune cells that carry out attacks and defend against pathogens.

To increase the number of healthy bacteria and for them to deliver their benefits, they need 'food' in the form of probiotics that are found in abundance in breast milk.

Babies over six months who are no longer being fed breast milk won't necessarily lose out because this is also found in some milk formulae.

When the healthy bacteria ingest these probiotics, they produce short chain fatty acids that function as an energy source for intestinal cells, to create mucous which acts as a gut barrier to infections and allergens trying to enter the bloodstream.

Brought to you by MAMIL GOLD

This article was first published in Mind Your Body, The Straits Times on Jun 4, 2008.