Doctors and other people alike say weather change make people sick. Hence never got help that way.

what is the pathology (IE what about the changes do doctors and other people say makes people sick, and in what way do they say it makes people sick)?

e.g. what is happening on a physical/molecular/cellular/biological level when weather changes make you sick, and what type of sick (do you get cancer, vomiting, contract smallpox, etc.?)