Most public water sources use chemicals like chlorine to treat water for bacteria. A small trace of chlorine in drinking water is considered safe, since the human body can filter it out. But in a steam shower, when water becomes gas, it can pose a risk, since the chlorinated water is being breathed in instead of ingested. To lessen the risk, crack the shower stall door slightly and have a vent turned on in the bathroom. You can also invest in a showerhead with an integrated filter to help reduce the presence of chlorine.