 However the Modalities or Physical Agents often have a certain setting or prescribed conditions such as specific temperature, material used, duration of application and positioning that make affect the efficacy or even safety of home use, thus the need for instruction prior to use.Each Physical Agent or Modality has a different contraindication based on how the tool affects the normal physiologic function of the body and how the tool affects the type of condition possessed by the site to be treated on the patient/client of the PT.Improper and uninformed use of these modalities can sometimes cause severe irreversible damage.