One of the main factors that determine indoor air quality is Temperature

As well as causing discomfort, indoor air that is very cold or hot is highly unhealthy. Cold weather acts as a vasoconstrictor, which means it narrows blood vessels.  
​Air that is too warm, for example, aggravates the effects of insufficient humidity.
When temperatures get too hot, your body has defense mechanisms that kick in to keep your internal temperature steady. These include:

• sweating
• increased respiration
• altered blood circulation

Sweating is an important one, and is greatly impeded by too much humidity in the air. Sweating cools the body when the moisture evaporates from the skin. However, when the air is already saturated with water vapor (as it is when humidity levels rise to 70 percent and higher), sweat can’t evaporate. So instead of cooling down, you just feel hotter and stickier.
At that point, the body is forced to resort to other means to try to cool off. That’s why you may notice yourself breathing more rapidly as you get increasingly hotter. Your heart pumps more blood to your extremities, and less to your internal organs and your brain. That’s why you feel sluggish and foggy. You may begin feeling light-headed or even faint. You may also feel muscle cramps, especially in your legs.
With the loss of fluids, salt and electrolytes, the body overheats. Eventually, if your body can’t maintain temperature, you can develop heat exhaustion or heat stroke, which can be fatal.

​​
(GreenFacts- Facts on Health and the Environment)