Hot tubs are a great way to relax and invigorate after a hard days work. But regular hot tub use could be making you sick according to some experts. An illness called "Hot Tub Lung" comes with a host of symptoms ranging from mild to serious and is caused by the bacteria growing in the slime (called biofilm) which develops on the surface of hot tubs as well as in the piping and equipment that circulate the hot water. And as if that is not enough, the same slime also appears on condenser coils of air conditioners and in duct work providing a safe place for bacterium to hide and grow.
According to researchers regular cleaning of hot tubs can remove the slime. But the system has to be emptied, dried and then scrubbed using strong disinfectants. However, cleaning might not be enough. Once inhaled, these bacterium take up residence in the lungs, perhaps for life. In a normally healthy person they present no danger. But as the person ages or becomes run down they can cause some very serious damage. You can get more information from Montana State University's Center for Biofilm Engineering.