My friends smoke around me a lot, but I don’t smoke, should I be worried for myself?

Yes, secondhand smoke can be just as dangerous as smoking a cigarette yourself. Every year, secondhand smoke causes over 30,000 deaths. Secondhand smoke exposes you to over 7,000 chemicals found in tobacco smoke, and approximately 70 that can cause cancer. Secondhand smoke increases your likelihood of suffering from heart disease, lung cancer, and stroke.
There is no way to be completely safe from secondhand smoke, and the only way to reduce risk is if you stop hanging out around smokers or if your friends stop smoking. Be adamant and clear about your wishes that your friends not smoke around you, or be strict with yourself and not hang out with them when they smoke. Also, inform your friends that they are harming their health as well as yours when they decide to smoke.
For more about the dangers of secondhand smoke, visit: https://www.cancer.org/cancer/cancer-causes/tobacco-and-cancer/secondhand-smoke.html