In 2026, medical professionals identify several key "red flags" that may indicate an immunodeficiency or a weakened immune response. One of the most common signs is frequent and slow-to-heal infections, such as having more than four ear infections in a year or chronic sinusitis. Another major sign is persistent fatigue; when the immune system is struggling, the body diverts massive amounts of energy to its defenses, leaving the individual feeling exhausted even after sleep. Digestive issues are also a significant indicator, as 70% of the immune system is located in the gut; frequent diarrhea, gas, or constipation can signal a lack of beneficial bacteria or an overactive immune response. Other symptoms include slow wound healing, where minor cuts take weeks to close, and an increased susceptibility to common colds that last longer than the typical 7-10 days. In 2026, doctors also look for autoimmune-related signs like joint pain or skin rashes as indicators of an "imbalanced" immune system.