What should we do during prayer if we catch a cold?

It is permissible for a worshiper to use a handkerchief when needed, based on what scholars have stipulated regarding the permissibility of minor movement in prayer out of necessity. This is supported by the Prophet's action, peace and blessings be upon him, when he removed his sandals during prayer, and his prohibition of spitting in front of him in the mosque, followed by his explanation of how to spit into one's garment.

Blowing one's nose should be done with the left hand, because Islamic law has designated the right hand for honorable matters and the left hand for matters involving impurities and the like. As reported by Aisha, may Allah be pleased with her, the Prophet, peace and blessings be upon him, liked to begin with the right in all his affairs. His right hand was for his purification and food, and his left hand for his private needs and anything involving impurity.