What are the symptoms of a weakened immune system?

Recurrent infections are the most recognisable sign of a weakened immune system. These infections return more often than normal, respond poorly to antibiotics, last longer, follow a more severe course, or are caused by pathogens that do not cause disease in healthy people, such as certain fungi or mycobacteria. This applies to both congenital and acquired forms of immune deficiency.

In addition to infections, hereditary forms of immune deficiency can also produce notable skin manifestations: hair loss, small haemorrhages in the skin, chronic skin infections, eczema-like rashes, unusual pigmentation, and wounds that heal poorly or slowly. These features sometimes help doctors reach a diagnosis earlier.

A weakened immune system can also, paradoxically, lead to conditions in which the body attacks itself. Think of autoimmune diseases, chronic inflammation, and allergic reactions. The immune system then overshoots, while at the same time failing to provide adequate protection against infections.

A less well-known but serious consequence is a greatly increased risk of cancer. In people with a congenital immune deficiency, this risk can be up to ten thousand times higher than in healthy peers. This is likely an association rather than a proven causal relationship, but its magnitude is large enough to take seriously.

In more severe, combined forms of immune deficiency, where multiple components of the immune system are affected simultaneously, complaints can be wide-ranging: persistent diarrhoea, respiratory tract infections, and very serious infections caused by pathogens that a healthy body handles with ease. The severity and breadth of the complaints give an indication of how deeply the immune disorder runs.