of an extremity is a serious condition. This should be evaluated by your primary doctor
. While there are many causes of this that are not concerning, there are some which would require intervention. Again, see your doctor.
Numbness is often a sign of nerve problems. Medically known as neuropathy, nerve problems come in two broad categories. The most common is a local compression of the nerve. This can happen anywhere along the nerve's course -- from the back where it exits the spinal cord all the way to the foot itself. If you have any back pain, hip pain, leg pain or any other way to localize the potential problem -- this could help. Nerve compression is not an emergency unless there is weakness -- if this is the case see your doctor urgently. In addition, loss of bowel or bladder function can indicate nerve compression and should call for an emergent evaluation.
The other general category of neuropathy is diffuse inflammation of the nerves. Often the longest nerves (those to the foot) get effected first. Diabetes, nutritional deficiencies (especially vitamin b12), Lyme disease, syphilis, myeloma, thyroid disease and alcohol toxicity can all cause neuropathy.
Talk to your doctor. This should be evaluated. Good luck!