Why does smoking usually cause raynaud's phenomenon?

Nicotine constricts: Nicotine constricts blood vessels, so smoking can worsen raynaud's symptoms. Caffeine can also worsen raynaud's symptoms.

It usually doesn't: There are people with raynaud's where smoking makes it much worse, and people who only get raynaud's after smoking. But smoking causes blood vessels to constrict in all people, just not to the extent you see in raynaud's where fingers turn blue, white and/or red. In people with raynaud's disease or phenomenon who smoke, they are at higher risk of serious vascular problems - heart attack, stroke.