okay, there IS this thing that when you lower your body temperature too much your defenses lower. In lowering your defences there is a higher probability that you will catch viruses coming from other people.
Viruses are more frequent in winter (thats why people hypothesise that cold is THE issue) because people spend more of their time inside their homes, where viruses are spread most about in being in closure and cosy-like (where viruses are most present in- which is why school is also a germ pool because of its closure and MANY family viruses inertwined).
So, not wearing a jacket, or going outside with your hair wet will get you colder, but it is not the cause for getting a cold, unless again, the temperature is at an extreme-like where your defenses lower. If your lucky at that point to not be around people with viruses -you're good
- I actually read a magazine article on this !