What is the main cause of numbness in hands?

Carpal Tunnel: Carpal tunnel syndrome is probably the most common cause of "numbness in the hands". This occurs when the median nerve gets compressed in the wrist. Other causes include compression of the median, ulnar, or radial nerves in the wrist, elbow or arm. Compression of the nerves leaving the neck and peripheral neuropathy are also common cause of numbness.

Lots: But common is carpal tunnel syndrome and cubital tunnel syndrome.