Can stress (or anything other than the allergen) be a factor in the frequency or severity of a dust mite allergic reaction?

You bet: Sress can be a factor in each and every disease idirectoly, sress ( ulcers, headache, adrenal outpore, obesity and so on) under stress you donot clean the house and then balme the allergens. So find out the cause of sress and work on, get rid od carpet in the bedroom, where you inhale dustmite for 8 hrs costantly.

Stress worsens: Our bodies are so complex, and we really only understand a fraction of how our bodies' systems interact with our environment. In general, chronic ongoing stress seems to worsen many illness. So yes, i'm sure stress has the potential to worsen allergy. It's good to make a concerted effort to lessen overall stress. See stress reduction techniques on health tap.