Here's why:

* Metabolism: This is the sum of all chemical processes that occur within the body to sustain life. These processes, like breaking down food for energy, generate heat as a byproduct. This is the primary source of our internal body temperature.

* Other sources: While metabolism is the biggest contributor, there are other sources of body heat, including:

* Muscle activity: When muscles contract, they produce heat. This is why you feel warmer after exercise.

* Sun exposure: The sun's rays can warm the skin, contributing to overall body temperature.

* External environment: Being in a warm environment can increase body temperature.

Let me know if you have any other questions!