I was diagnosed with HES 5 years ago after being diagnosed with breast cancer. I was always very healthy until then so did not need blood tests regularly like they want with a cancer patient. They then discovered I had extreme lives of eosinophils. All other test ruled out parasites, infections, genetics, allergies, etc. I was seen by some great doctors at Mayo Clinic and they found eosinophils tissue in my esophagus. But I do not have any other symptoms. Praise God! I may have had this for many many years and it went undetected. My doctors test my blood every 8 weeks and also watch my heart. I hate think some day HES will start to attack my good organs. I'm not sure is anyone else has experienced no symptoms. If so, I'd love to hear from you.