18 Hidden Causes of High Neutrophil Counts That Doctors Want You to Know

11. Smoking

Cigarette smoking has a profound effect on the immune system, and one of its lesser-known consequences is neutrophilia. Research has shown that chronic smokers tend to have higher white blood cell counts, including an excess of circulating neutrophils. This occurs because smoking introduces harmful chemicals into the lungs, triggering a constant low-level inflammatory response. Neutrophils, as part of the body's first line of defense, are continuously produced in greater numbers to combat the perceived threat. Over time, this persistent inflammation can contribute to chronic lung conditions such as chronic obstructive pulmonary disease (COPD) and increase the risk of cardiovascular disease. Interestingly, former smokers often experience a gradual decrease in neutrophil levels after quitting, as the body begins to recover from inflammation. The link between smoking and elevated neutrophil counts highlights yet another reason to consider quitting—beyond lung health, it directly impacts overall immune system function and long-term well-being.