What physiological reactions occur after quitting smoking?

After quitting smoking, the body undergoes a series of predictable physiological changes as it begins to heal from the damaging effects of tobacco smoke. Within 20 minutes of cessation, heart rate and blood pressure begin to normalize. Within 12–24 hours, carbon monoxide levels in the blood return to baseline, improving oxygen delivery to tissues. By 48 hours, nerve endings start regenerating, often leading to improved senses of taste and smell. Between 2–12 weeks, circulation improves and lung function begins to increase, with measurable gains in forced expiratory volume (FEV₁). At 1–9 months, ciliary function in the airways recovers significantly, reducing mucus accumulation and decreasing cough and shortness of breath. After one year, the risk of coronary heart disease drops by approximately 50% compared with that of a continuing smoker. Long-term benefits include a 50% reduction in stroke risk after 5 years, and after 10 years, the risk of lung cancer falls to about half that of a current smoker. These changes reflect the remarkable capacity of the human body to repair itself once exposure to tobacco toxins ceases.