"It's not so much the heat, as it is the humidity.
A phrase that rings true in almost every home. When it's muggy outside, it's muggy inside. And excess humidity can make you miserable. You can literally see, feel and smell it:
Left unchecked, excess moisture can cause:
"As many as 10 percent of the general population and 90 percent of people with allergic asthma are sensitive to dust mites. Recent studies in the United States suggest that at least 45 percent of young people with asthma are allergic to dust mites."
-American College of Allergy, Asthma and Immunology