My wife is from Guangdong province in the south east region of China. The temperature there most closely resembles Florida, USA. It is usually in the 90s during the summer instead of sometimes. It is always humid and feels tropical.

My wife, her friends and family routinely comment on how incredibly hot it is in China. They say people often don't even go outside because it's so hot. They say it is not like Minnesota, but much worse.

My question then... how? Is this merely perception of growing up in a tropical environment without artificial climate control or is there science that backs up their claims? If our regions are the same air temperature with similar humidity and dew points, I don't understand how it can feel so much hotter there.

It might be the case that temperatures match up at some points, but based on the classifications/geography of both areas, it would seem that Guangdong experiences more humidity and much longer warm periods, which combined would raise the Humidex (https://en.wikipedia.org/wiki/Humidex) above that of Minnesota.

For more information on the Koppen-Geiger classification, https://en.wikipedia.org/wiki/K%C3%B6ppen_climate_classification

[In Guangdong] It is usually in the 90s during the summer instead of sometimes. It is always humid and feels tropical.

You're saying that sometimes Minnesota is as hot as Guangdong usually is. Thus (based only on this info) Guangdong probably has a higher mean temperature. Assuming there is some variability around that mean, it seems likely that Guangdong also has a higher maximum temperature. Thus, Guangdong might be perceived as hotter.

Cultural factors might also contribute to the perception of difference, such as the type of clothing worn, the prevalence of air conditioning, or the activities that the people in question are typically undertaking in each place.