Question: Based on your observations, why do you think more females than males are diagnosed with CFIDS, FM, etc.? Hormones? Reply: Others have also thought about this, and most have come to the conclusion that it has to have something with the hormone status. An interesting observation is that pregnant females often lose their CFS symptoms as their estrogen levels drop, only to have them slowly return after pregnancy as their estrogen levels rise. Also, many microorganisms, such as Mycoplasma spp., are very sensitive to estrogens. This would explain the loss of symptoms during pregnancy when estrogen levels are very low. Men only express estrogen at very low levels and testosterone at high levels. It would be interesting to see if men with low levels of testosterone (this hormone declines with aging) are more likely to have CFS.