Damp or cold air cannot by itself cause a cold. An indispensable factor in the catching of cold is the presence of germ infection and, whatever hardships or exposure we undergo, they will not result in an ordinary head cold provided the air is free from infective germs.
Investigators in the cause of science have exposed their naked bodies to direct draughts of freezing points, having first attained an over heated condition by violent exercise and yet, though the experiment was tried over prolonged periods the result which might have been expected, viz, a cold did not appear.
There is however, a way in which bad weather, conditions can play a more definite part in cold causation, and that are alternated with unhealthy atmosphere. If we get thoroughly chilled, with wet feet, and then go into confined surroundings and sit or remain in these conditions, we are in a fair way to catching a cold. This is because the blood is diverted from the cold extremities where the arteries are contracted, to the head, which tends to become relatively congested. This congestion, which is increased by the hot stagnant air surrounding the head causes the mucous membrane of the nose to become unhealthy and swollen, and lowers its resistance to the germs of infection which now surround it. If the feet were first warmed by a change of shoes and stockings and by brisk massage, the body would become more evenly heated, and though the atmosphere would still be an unfavourable one, less harm would result.
Entering a stuffy closed room from the fresh air of outside, similarly, causes a cold by adversly affecting the mucous membrane of the nose and lowering its power of resistance.