“According to the hygiene hypothesis, people who grow up in areas with high levels of sanitation lack normal evolutionary exposure to microbes, pollen and other microscopic things in the environment. The lack of that exposure negatively affects the development of their immune system, according to the hypothesis.” Could Getting Dirty and Being Exposed to Germs Boost Your Health?, usnews.com
Hand sanitizer and soap affects your natural fauna, that are accustomed to living on your skin.
Study: Washing your hands — even without soap — is more effective than hand sanitizers for flu prevention, minnpost.com
The Effect of Handwashing with Water or Soap on Bacterial Contamination of Hands
Comparative efficacy of hand hygiene agents in the reduction of bacteria and viruses
Effect of handwashing agents on bacterial contamination
Somewhere, I read a research article that said that water alone reduced bacteria on the hands to 96 or 98 percent, where using soap reduced 99.5%, or something like that. Can't find that anywhere.
“However, many studies have demonstrated that, on average, only 40% of health care workers' contacts with patients result in appropriate hand hygiene.” https://www.sciencedirect.com/science/article/pii/S0196655304005875