PEMF frequencies break down into two basic groups, below 100Hz and above 100Hz.
Frequencies below 100Hz are referred to a "cell signaling" frequencies and will help with disease that originates from within the body (breakdown of normal body functions).
They tell your cells to do things they would otherwise be doing naturally if your body systems were working optimally but for one reason or another are not.
This could be caused by many things such as compromised immune system, lack of proper diet, injury (such as a broken bone), environment, and so on.
Frequencies in this range can aid in improved blood circulation, better digestion, relieving inflammation, reducing pain, and the healing of body systems that are not damaged beyond healing.
For example, the FDA has approved the use of PEMF for bone healing. The frequency used for this is 76.6Hz. Although there are many cell signaling or healing frequencies above 100Hz, the most basic and general wellness ones are in the 100Hz and below range.
In the frequencies above 100Hz you find the "resident frequencies" of pathogens. If you have disease that originated from outside the body (bacteria, viruses, or generally all pathogens), the only way PEMF will affect them is to use the frequency that matches their resident frequency. It causes them to vibrate to the point of destruction. The resident frequency of virtually all pathogens is well above 100Hz.