I do not have Reynaud's and really very few people do. About 4% of the population may have some symptoms. Reynaud's disease is a constriction of the blood vessels in the hands and toes which causes a feeling of cold and numbness. Reynaud's is considered to be idiopathic, that is no known cause. I am sure you know this, but other readers may not.
The most common factor associated with Reynaud's disease is smoking. For everyone who does have symptoms of Reynaud's, they need to stop or never start smoking tobacco. This will just make the constriction in the blood vessels much worse. Again, this is not a definite cause, but very strong association.
Other factors are caffeine, certain medicines and estrogens. However a New England Journal of Medicine article in August 2016 says that there is not any solid evidence that these should be avoided.
The simplest treatment is to avoid cold temperatures. If the condition persists, your doctor can prescribe certain medications that will lessen or prevent future attacks of vascular constriction.