SMOKING or inhaling toxic fumes including vehicle exhaust is a major risk factor. Tobacco smoke contain thousands of chemicals, at least 70 of which are listed as carcinogens, for example:
Radioactive elements (e.g., uranium)
PAHs (Polycyclic aromatic hydrocarbons)
Chemicals take up space that would ordinarily be occupied by oxygen, which leaves the brain slightly anoxic. Prevention strategy? Never smoke; if you smoke now, stop! Avoid inhaling side-stream smoke if at all possible. . .