What makes someone ever have a low body temperature?

Thyroid: Many people are on the low end of normal. It could be your normal or hypothyroidism. (low). It is most likely fine. I would ask what you are calling low. Many people have a normal body temperature but think they are low or high based on incorrect information they have been given. You can also be low due to environment. "normal" for adults is generally considered above 96.5f-99.5f.