Smoking cigarettes is extremely dangerous and causes millions of deaths each year. Cigarettes contain over 4,000 chemicals, including 40 known carcinogens. They are intentionally designed to be highly addictive by adding chemicals like ammonia and substances that increase nicotine absorption. Quitting smoking is very difficult due to the addictive nature of nicotine, but the health benefits of quitting can be seen shortly after stopping. Withdrawal symptoms typically peak within a few days and can last for months.