Q: why is my macbook air getting so hot

First try a SMC reset:

https://support.apple.com/en-us/HT201295

If there is no change, install a temperature/fan speed monitoring application.

Set Activity Monitor to ALL PROCESSES and CPU to display values from high to low.

Post images of both for review when the MBA gets hot.

Run an Apple Hardware Test:

https://support.apple.com/en-us/HT201257

Note that an error free AHT is NOT conclusive.

Ciao.

That is not a good sign.  You may have to have the MBP evaluated at an Apple store genius bar.  It will be done for FREE.

Have you tried my other two suggestions?

Ciao.