Possible Causes for low body temp when ill? Sepsis and thyroid can cause lower body temps. Janq - Do you normally have a temperature of 98.6 F. ? Some people have a normal temperature that is lower than the "typical normal". I know my temperature when not sick is normally any where from 95.8 to 97. When I'm ill the temp goes "up" to anywhere from 98.6 to 101 (that's really high for me.). Check with you md and find out what your "normal' is. Then go from there.