Hi.. The recent air conditioned are relatively safe in a normal person if it is maintained properly and is from standard company.. The real problems posed by the air conditioner are in a few who have recurrent sinusitis.. It can aggravate these minor flu and sinusitis problems.. Apart from this it can cause few viral pnemonia and a specific infection of the lung known as legionaires disease. These infections are known to occur if the filters used are not maintained properly to the standards.. Explanation to these details are provided in this link http://www.essortment.com/all/airconditioning_rvht.htm