Sorry for the confusion, boiling an herb first will prevent bacterial contamination in an overnight infusion, but as was mentioned Marshmallow is not usually boiled, it sits at room temperature for 4-6 (or more) hours. So it depends on your Marshmallow root, if it is contaminated with pathogenic bacteria it could be a problem. Especially in people who are immunocompromised. Still many people do this on a regular basis and do not have any problems, so I think it is a rather uncommon issue. I hope that helps, there is not definite answer.