Immune system weakness occurs when the body's defense mechanisms are not functioning optimally, making it harder to fight off infections and diseases. This can be caused by various factors, including poor nutrition, chronic stress, certain medications, and underlying health conditions like HIV/AIDS or diabetes. When the immune system is compromised, individuals may experience frequent illnesses, prolonged recovery times, and increased susceptibility to infections. Maintaining a healthy lifestyle, including a balanced diet, regular exercise, and adequate sleep, can help strengthen the immune system and improve overall health.