Infections such as flu, pneumonia, or urinary tract infections raise blood sugar by triggering stress hormone release.

When the body fights an infection, it activates the fight‑or‑flight axis. Hormones like cortisol and adrenaline signal the liver to produce more glucose, giving immune cells quick fuel. This mechanism is described in multiple sources: winter viruses and colds add stress that raises blood sugar, and severe infections such as UTIs, pneumonia, or influenza are noted as contributors to hyperglycemia in non‑diabetics. The effect is temporary but can be pronounced during acute illness.