Do facemasks and social distancing weaken the immune system because of reduced exposure to pathogens?

Question

I am operating under the following premises:

• The immune system needs to be constantly trained by exposure to pathogens to remain effective.
  • I remember having read that the reason why little children are frequently sick: this is how their immune systems build to let them stop being sick that often. Therefore, frequent colds are actually beneficial.
• Facemasks are designed to impede the spread of airborne pathogens. Their recent widespread use is caused by the Covid pandemic, however their side effect is that they impede other disease as well. Same can be said about social distancing.
  • I asked a physician when would wearing masks stop. In response she praised anti-covid restrictions for accidentally also solving the problem of the common cold and flu and said we should never stop wearing masks.

Doesn't it follow that restrictions such as facemasks and social distancing weaken the immune system by preventing airborne pathogens to reach it?

I asked about this topic somewhere else but in response I was rebuked for spreading conspiracy theories. I don't think this is what I'm doing. In no place did I cite conspiracy theorists? Some mainstream media say similar things to what I wrote in the premises. This Time article for instance.

Answer 1

Although this idea gets tossed around a lot, it's a bad question on this level of generality because

1. Individual vs population immunity are not the same thing. Even assuming the population eventually benefits from more individuals being exposed to a pathogen... that's not a given it's going to happen in any time frame an individual might care about. Eventually, the pathogen may be driven to extinction in the population... or it might not... because it co-evolves. Smallpox and tuberculosis (just to pick two airborne examples) have been with humanity for thousands of years. Few would think it's sensible to deliberately expose yourself to either (in their fully infections form) to "prevent weakening" your individual immune system.

2. So maybe the argument just refers to less dangerous pathogens like common colds and influenzas, which were circulating more widely. Unfortunately, it's too early to say what the "rebound" effects are going to be like once people stop wearing masks (although in many politically recalcitrant areas, they never really took them up--so that might actually prove an interesting comparative "natural experiment", going forward). The few data that exists so far suggests that once people (in particular children) stopped distancing or wearing masks there were some temporally clustered outbreaks of rhinovirus and RSV infections. Whether there's substantial extra disease burden from these in the long run can't be known at this point; you'd need data at least year-on-year, but preferably for several years after people stop wearing masks or socially distancing. (Several years because common colds and influenzas have substantial year-on-year variability simply driven by their own strains.) And even then, assuming there is such a long-term increase, there would be the issue of what scenario would have been more preferable: more Covid-19 now vs more "common colds" later.