A normal healthy individual can also get infections. However, serious repeated infections may suggest that there is something wrong with the child's immune system and that may be leading to repeated serious infections.

Immune system consists of skin, the nose and airway cells and finally various white blood cells (WBCs) in the blood. The skin is the most important barrier for infection. An intact skin prevents entry of most of the germs and any break in the continuity of the skin can lead to infection. Thus, infections are commonly seen in patients with burns.

Our next most common defense mechanism is the airway passages through which we breathe. The air which we breathe may contain plenty of germs and if they were not captured and expelled from the body would lead to different types of infections. The air passages contain a special type of hair called the cilia and also have mucus lining it. Thus any germ is trapped in the mucus and by beating of the cilia is moved upward towards the mouth and expelled out by the cough mechanism. Thus, these 2 most important barriers prevent most of the infections in the human body.

However, if a germ bypasses these 2 defense mechanisms then there are certain cells in the blood (WBCs) that fight these germs. These cells consists of specialized cells called as neutrophils, T lymphocytes, B lymphocytes and monocytes. B lymphocytes also release certain proteins called as antibodies that fight against most of the bacteria. There are 5 major types of antibodies - IgA, IgG, IgE, IgD and IgM. T lymphocytes fight against mainly viruses and fungi.

Thus, any defect in these specialized cells can lead to defective immunity and immune deficiency disorders that may lead to frequent serious infections.

When to suspect an immune disorder?
One may suspect an immune disease in a child in the following situations:
 Repeated ear infections or sinus infections.
 More than 2 pneumonias in a year
 Recurrent, deep skin or organ abscesses
 Persistent thrush in mouth after one year of age
 A family history of primary immune deficiency.
 Unusual manifestation of a common infection
 Infection by an unusual organism