Smoking
Smoking cigarettes is bad for many reasons. Besides increasing your risk of lung cancer and many other respiratory problems, it can contribute to the development of a brain aneurysm. This is because smoking alters how your blood vessels normally function. [4]
It damages the walls of your arteries by filling them with plaque, making them stiff and less elastic. Chemicals present in cigarettes cause blood clots to form in the blood vessels as they thicken. Nicotine, one of the many chemicals present in a cigarette, causes the blood vessels to narrow.
These effects contribute to an increase in the pressure of the blood flowing through the vessels. Arterial hardening and inelasticity make it easy for the blood coursing through the vessels to hammer on weaker spots in the blood vessels and expand them. If this happens in the vessels of the brain, an aneurysm may develop with time.