My daughter and I recently attended the Macy's Thanksgiving Day parade. It was 35 degrees F and we stood outside for several hours. When we went inside a restaurant, my daughter took off her glove and showed me that her middle finger had gone completely white. She said this had happened to her before. What could this be?

A: There are several possibilities.

The most likely explanation is Raynaud's phenomenon. This is a condition in which blood flow to the fingers is temporarily impaired. Sometimes other parts of the body are affected, such as the toes, ears or nose.

Raynaud's is thought to develop because of an exaggerated constriction of the arteries that supply blood to the fingers.

We all have nerves that send signals to the small arteries of the fingers instructing the arteries to open or constrict. For example, the arteries normally narrow when you're cold. This is the body's way to conserve heat.

For unknown reasons, the tendency for arteries to constrict in the cold is exaggerated in people with Raynaud's. After being exposed to the cold, artery constriction initially leads to whiteness of the fingers, then blueness and then, as the artery opens up again, redness. Usually this sequence occurs over a number of minutes and the finger soon appears normal again. Besides cold, emotional stress and certain medications can also trigger this reaction.

Although Raynaud's can be associated with scleroderma, lupus or other rheumatic diseases, at least 90% of people with Raynaud's have no other associated condition.

The first choice of treatment is simply to avoid the cold. Here are some tips:

  • Wear mittens
  • Bundle up before going out in the cold
  • Avoid the freezer section of the grocery store (or wear thick mittens there)
  • Turn up the thermostat

For more severe Raynaud's, medications are available that can help.

Another possible cause of a white finger is frostbite. However, when frostbite is severe enough to cause an entire finger to turn white, other fingers are usually red and swollen, and the white area may be hardened. Other symptoms are typically present such as:

  • Numbness
  • Severe pain
  • Ulcers or blisters
  • Eventually, darkening or black discoloration of the fingertips

Also, frostbite is not reversible within minutes the way Raynaud's phenomenon is.

Finally, a white finger could be related to an artery blockage. This may occur with a blood clot. However, if a blood clot was the cause, the finger would soon turn dark and become quite painful. This is a very unlikely cause in a 15 year old.

Since this has happened before, it's a good idea to bring it to the attention of your daughter's doctor. After a review of her symptoms and a physical examination, there may be little more to do other than avoid situations that trigger Raynaud's.

Robert Shmerling, M.D., is associate physician and clinical chief of rheumatology at Beth Israel Deaconess Medical Center and an associate professor in medicine at Harvard Medical School. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program and has been a practicing rheumatologist for over 25 years.