what is HFA?

Source: U.S. Food and Drug Administration (FDA)

HFA means hydrofluoroalkane and is the chemical used to propel the medicine out of the inhaler.
Examples of HFA inhalers are:
Proventil HFA, ProAir HFA, Ventolin HFA, Advair HFA, Xopenex HFA, Atrovent HFA
These inhalers are used to treat shortness of breath, wheezing, asthma.

The chemical HFA does not have anything to do with the medicine itself. This chemical is just to propel the medicine out of the inhaler into the patient's mouth.

It is worth noting that the previous chemical CFC to propel the medicine out of the inhaler was harmful to the Earth's ozone layer. In turn, the Food and Drug Administration, in 2009, began to require that all inhalers use the chemical HFA because HFA is considered to be a safe, effective, and environmentally-friendly alternative.