Smoking harms the immune system by exposing the body to thousands of toxic chemicals that damage cells and reduce their ability to fight infections. It lowers levels of protective antioxidants, like vitamin C, and weakens immune cells such as white blood cells, making it harder to defend against viruses and bacteria. Smokers are more prone to illnesses like pneumonia, flu, and respiratory infections, and wounds or injuries often take longer to heal. Over time, smoking can also trigger chronic inflammation, which further disrupts immune balance. Quitting smoking allows the immune system to gradually recover and function more effectively.