Immune deficiency occurs when the immune system is weakened or not functioning properly. There are two main types - primary and secondary immune deficiency. Primary immune deficiency is present from birth and can involve deficiencies in phagocytic cells, B cells, or T cells. Secondary immune deficiency develops due to external factors like infections, malnutrition, or drugs. Common symptoms include recurrent infections of the skin, lungs, sinuses and other organs. Diagnosis involves medical history, exams, and lab tests. Treatment depends on the underlying cause but may include antibiotics, immunoglobulin replacement therapy, stem cell transplants, or gene therapy.