The only way listening to Solfeggio Frequencies might be harmful is from the volume.
You see, listening to any sound greater than – 60db’s has the chance to harm your hearing or cause tinnitus. Always be cognizant of the volume level you are listening not just Solfeggio Frequencies, but all music to.
There are no shown negative benefits that comes from listening to Solfeggio Frequencies, or retuned music.