Today I learned about wet bulb temperature:
It’s the lowest temperature in a given environment that can be reached by evaporating water (e.g. sweating). At 100% relative air humidity the regular ambient temperature and wet bulb are the same. At lower humidity wet bulb is lower because the air can still absorb additional vapor. Humans generally can’t survive for long at wet bulb temperatures of 35°C (95°F) and higher.
This measurement might become much more widely used as dangerous heat conditions become more common.
https://en.wikipedia.org/wiki/Wet-bulb_temperature
Edit: there’s newer studies that indicate the wet-bulb limit for humans to be a lot lower even https://journals.physiology.org/doi/full/10.1152/japplphysiol.00738.2021