Humidity 90% in baby room. the dehumidifier fails to decrease the humidity. what to do? may a bigger dehumidifier? how is the high humidity harmful?

If only in that room: This would suggest the presence of water intrusion in that room and this needs to be remediated. Need to keep a window open for a few hours each day also to air out the room since molds thrive in humid and stagnant environment. Take care of this before your baby gets sick. Living in a humid environment has been linked to more respiratory diseases and development of asthma etc.