Is it hotter in different places with the same air temperature? I am from (and live in) Minnesota, USA. In the summer here it always reaches temperatures in the 90s (F) for periods of time but not every week. The humidity is often high and the dew point often tropical.

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.
While perceptions about the climate can have an effect on how we react to our environment, Guangdong and Minnesota are fundamentally different climates altogether. Using the Koppen-Geiger climate classification system, Minnesota is mostly a Temperate Continental (Dfb/Dwb) climate, meaning that is has warm summers and long cold winters, while Guangdong is a Humid Subtropical (Cfa/Cwa) climate with hot and wet summers and a short dry winter. The classification is largely based on monthly average temperatures and precipitations based on climate normals (~30-year periods).

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