are those mold? and are these dangerous?
It looks like mold / mildew yes it can be killed with a bleach &amp; water solution or a hydrogen peroxide and water mixture. Is it the “bad stuff” only testing will reveal that but to tell the truth that doesn’t look that bad. But killing it and keeping the area dry, making sure the vent fan is on when using the shower / bath will help get the moisture out that is allowing the mold to grow. I prefer 3% hydrogen peroxide and water AAA (always add acid to water to prevent an exothermic reaction.