Steroids have the ability to suppress your immune system. Thus, allowing the fungus to grow even more. That was my question in the first place.
They do for me. I never recommend the combo since you're not evening coughing out the phlegm you've just loosen. Doesn't make sense. Rather I always suggest mucinex for productive and dextro for nonproductive. Never the combo.
Yes, using the steroid portion alone would suppress the immune system and cause a faster spread of the offending organism. However, the combination works differently. The antifungal gets rid of the organism slowly, while the steroid provides rapid relief of the symptoms (itchiness, redness, etc).
If the person only uses the antifungal portion, the infection rash will be a lot more itchy, the person will scratch it a lot more, and probably cause it to spread.
http://www.aafp.org/afp/2002/0515/p2095.html
ANDREW WEINSTEIN, M.D., M.P.H., and BRIAN BERMAN, M.D., PH.D., Topical Treatment of Common Superficial Tinea Infections.University of Miami School of Medicine, Miami, Florida.Am Fam Physician. 2002 May 15;65(10):2095-2103.
As for the Mucinex-DM combo, I don't have any articles about that on hand but personally I don't recommend guafensin at all since drinking H20 is more effective. (My only backup for this is what was on my professors lectures slide.)