What is the cause of raynaud's phenomenon (purple toes)?

See below. It is a constriction of the blood vessels on exposure to cold.
Raynauds Phenomenon. Secondary Raynaud’s is also known as Raynaud's Phenomenon which is caused by an underlying disease, condition, or other factor. Many things can cause secondary Raynaud's such as diseases and conditions that directly damage the arteries or damage the nerves that control the arteries in the hands and feet or Repetitive actions that damage the nerves that control the arteries in the hands and feet.

Related Questions

Can there be a relation between alopecia (hair loss) & raynaud's (purple coloured toes)?

Hmm. Do a web search. I do not think these two are related. But... Medicine is funny that way. There could be a rare association and both conditions are common - so... It is not surprising to see them together. But not related. Read more...

Raynaud phenomenon syndrome question. Is it really that or poor circulation?

See below. Raynaud's phenomenon describes a set of color changes in response to cold or stress. These are usually preventable and treatable. Poor circulation does not have those changes. Read more...
Color and location. Raynauds causes fingers to turn either white, blue and/or red usually in the cold. Poor circulation is different because it can affect palms and usually the border of the color change is a smooth transition. Raynauds usually has a distinct line between normal and blue /white. Read more...