We already avoid living in the interior of Australia, because living at temperatures of +50°C is just not very compatible with having body temperature slightly below +37°C. Same applies to the middle of Sahara desert. It's not impossible though, because the humidity is very low there, so, given a supply of water, you can cool by evaporation. At high humidity. you'd just die; such things happen during heat waves on the Indian subcontinent, for example.