Many people use antimicrobial soap to kill bacteria on their hands. However, overuse may actually increase the risk of infection. How could this occur?

Well observed. Let me explain how:

Antimicrobial products, such as soap and creams, contain antiseptic compounds, obtained from chemical, biochemical or natural sources.

All of them reduce the possibility of microorganisms surviving, by different means (pH imbalance, destruction of their membranes, induction of mutation, etc).

As you may have seen in the advertisements, these components only eliminate 99.99% of microorganisms. This means that there is always a small chance (0.01%) that some tolerant insulates could appear.

As a result of a continuous and excessive application of the same antiseptic over and over again, all microbes are eliminated less microbes those few tolerant. Being the tolerants, the only ones alive, all the offspring generated from them will carry the genes with tolerance to the next generation.

It is a clear example of genetic selection.