Does the sun help a common cold? How can sunbathing help relieve a common cold?

High temperature. Cold viruses thrive in low humidity and cold temperatures. They cannot survive at elevated temperatures. The sun bathing can be helpful to keep the temperature of your mucous membranes warmer.
No/It doesn't. The sun does not help a common cold. Sun bathing will not help a cold but it will predispose to skin cancer.