A small nodule has appeared on the back of my right hand, quite near the wrist. It feels firm, but is also slightly squishy. It seems to have appeared overnight. It is not painful, unless I press on it. I'm mystified, and so is my wife, who is a nurse.

Dr Fred Kavalier answers your health question:

You have a ganglion, which is a small cyst that has popped out from between the small bones that make up the base of the hand. The space between these bones is lined with a membrane that protects the surface of the bones and keeps the space lubricated. A ganglion forms when some extra fluid is produced by the membrane. Ganglions can be a bit sore, but they usually just sit there, causing no trouble at all. Eventually they disappear, as mysteriously as they appeared.

Please mail your questions for Dr Fred to health@independent.co.uk. He regrets that he is unable to respond personally to questions.