Have you been told that when you stay in cold environments especially wet ones, you are going to fall ill, or did you hear that path were you were told that cold environment would give you pneumonia? Quickly let me tell you that it is a myth and you would only fall ill as a result of pathogen and our body have great defense mechanisms against pathogens from snot, oily skins, cells that defend us all day, and even viruses.
When we discuss infection s fighting infection, the first thing that comes to mind isn't the skin or its associates (hair, nails, scales or feathers). But the skin and its associates are an animals first layer of defense for pathogens or its innate defense system. These outer layers are referred to as the integumentary system keeping the insides in and the outside out and with this it prevents the entry of pathogens into the body.
needpix
While our skin looks extremely naked compared to other mammals, it still performs a great job. It is a professional at regrowing and fixing itself. In some animals, Sebum is created on the skin. It is an oily mixture that is acidic, helping in killing pathogens. But since we need to eat, drink, breath, and pass out waste, we have openings that can allow for pathogens to enter into the body but our body thanks to evolution has prepared us for this. Where there is an opening, there is a protective barrier to keep safe and for most vertebrates, it is mostly a layer of mucus membrane containing immune cells and natural antibiotics.
Although the body actually have barriers to hold this pathogens in openings, they still sneak pass them getting into the body and this is where the immune system begin their jobs. For instance, Macrophages which are a type of white blood cell engulfs the pathogen, Natural Killer cells as their implies says it all that they are killers as they kill microbial infection and tumor cells by secreting poison on them. Inflammation is another way that the body acts to keep itself safe. The body begins to change its temperature to become hotter so it can destroy whatever pathogens are found inside the area. To do this, the site is red as a result of being filled with blood to fight the invader.
When our body is attacked by invaders, the pathogens do not give us symptoms right away, rather it is the body immune system that gives us the symptoms that we feel because it is fighting for us to be alive. But then there are cases where pathogens fly under the radar, getting into our body without being noticed. At this point they get into the body and start to reproduce and the body doesn't show any symptom leading to an asymptomatic infection. This happened with Covid-19 where people were infected but not showing symptoms.
Adaptive immunity is another type of immune response that we hold as humans. It has to do with identifying and remembering the pathogen in case of a next time. Understanding adaptive immune system is what has help scientists to be able to create vaccines. With vaccines, the body will start making antibodies to fight an almost similar pathogen compared to the real deal. This immune system after identifying and fighting the pathogen, uses the memory B-Cells to remember when next those pathogens or proteins get into the body again.
In all this, there are cases when the immune system begins to misbehave and in this cases, they begin to attack the body itself leading to what is referred to as auto immune disease. Overall, our immune system is great as a does a wonderful job warding off diseases and pathogens. The notion that cold weather directly causes illness is a myth. Our bodies are equipped with sophisticated defense mechanisms to combat pathogens, from the protective barriers of our skin and mucous membranes to the complex activities of our immune system.
Reference
https://www.mayoclinichealthsystem.org/hometown-health/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4863567/
https://www.ncbi.nlm.nih.gov/books/NBK279396/
https://healthtalk.unchealthcare.org/mucus-our-bodys-silent-defender/
https://www.nature.com/articles/ni1582
https://www.ncbi.nlm.nih.gov/books/NBK26921/
https://www.cancer.gov/publications/dictionaries/cancer-terms/def/t-cell
https://www.pnas.org/doi/10.1073/pnas.2109229118
https://www.nature.com/articles/ni1582