I'll say from personal experience, I found out that my body is actually awesome at responding to colds - I just don't let it.
Storytime - for pretty much all my life, I've had what I considered a pretty normal and functioning immune system. I would get a cold, feel how you felt for a few days or weeks, mostly just power through, and then I'd be back to normal.
However, in college I took 6 months off to hike the Appalachian Trail. This was great for a lot of reasons, but one thing I noticed (which everyone around me agreed on when I mentioned it to them), is that I'd pretty much stopped getting colds. For reference, trail life is not at all sanitary. Daily showers and grooming are the stuff of fantasy. Washing your hands after you take a shit is rare. If you frequent the small lean-to shelters along the trail to sleep (as I did almost every night), you will be sleeping shoulder to shoulder with other hikers with similar levels of hygiene. And it's not like we are somehow not catching and transmitting pathogens to each other. Every year, things like the flu or norovirus will rip through the hiking community, leaving 100 mile stretches of trail where you'll walk past dozens of hikers groaning in their tents (haphazardly set up just feet from the trail), with a pool of vomit just outside.
But the whole time I was on the trail, I never got a cold. As long as I wasn't sick sick, I felt very generally healthy. Why?
Well, the life I was living was very different than my normal life. I think I am decently healthy in my normal life. I eat a healthy diet and exercise regularly. But on the trail, I had a lot more things going for me.
- I slept a lot, in sync with my circadian rhythm. 8pm was widely agreed to be "hiker's midnight", since about 15 minutes after the sun went down, all the hikers would start feeling sleepy and decide to go to bed. I would usually knock out instantly, and then wake up at first light, groggily peer out my tent at the coming morning, take a piss, then roll back over and sleep for another hour or two.
- I was getting a lot of exercise. This exercise was rarely particularly strenuous, but every day I would wake up, shoulder my pack, and walk about 15 miles.
- I had a phone, but had no backup battery bank, mini solar charger, or anything like that. Cell reception in the hills typically oscillated between bad and nonexistant. So my phone almost universally lived in the bottom of a stuff sack inside my backpack. I would take it out maybe once every couple days to listen to a song or two before turning it off again to conserve prescious battery life in case of emergency. Partly this helped because it meant that I wasn't staring at a bright phone screen when I should be sleeping. But more than that, I think it helped because I wasn't constantly feeding my brain a stream of nee content. I spent almost my entire day, every day, hiking in the forest in silence with no distractions. All I had to entertain myself was noticing the environment around me, occassionally checking my map and digital watch to calculate how far to the next stream/shelter/trail junction/town, and whatever thoughts came up in my head.
- I spent pretty much all my time breathing fresh air. Most of the time I was in rural land with very little air pollution, and even when I did approach population centers, they tended to be, at most, medium-sized towns.
- When I wasn't hiking or camping alone, I was hiking and camping with other hikers. Trail life tends to dissolve the differences in class, age, national origin, political affiliation, religion, or anything else. Everyone shares a common interest - life on the trail - so conversation tends to flow easily. Trail talk tends to center around things hikers think about - food, water, miles, towns, shelters, gear, other hikers, weather, poop. Outside the rare individual who gives off bad vibes, everyone is welcome and welcoming, creating a general sense of community and support.
- I had a well defined goal, obvious steps to take to achieve it, and made progress every day. The goal: walk to the northern terminus. The plan: wake up, break camp, walk. Every day, I could lay down in bed and look at my map, celebrating the progress I'd made, seeing how much closer I was to some landmark like a town, a mountaintop vista, or a significant mile marker. With a clear goal like this and few other distractions, my sense of time dialated significantly - the present moment became paramount. The next few and previous few miles were all that mattered. Yesterday and tomorrow were significant markers in my mind. But the town I was in 3 days ago, I felt I hadn't seen in years. And when I started the trail? What I would do when I finished? That was another lifetime.
All these things, I think, contributed to my physical and mental health. And doing so, they either (a) improved my immune system enough that the common cold was stamped out long before my body had to create congestion to deal with it, or (b) my immune system wasn't overreacting to a relatively minor threat, and was simply taking care of these minor viral infections in the background without bothering me