Miconazole blocks the enzyme fungi use to make ergosterol, the fatty substance their outer wall is built from. Without it the wall leaks and the fungus cannot grow. At the concentrations reached on the skin it also damages the membrane directly, so against yeast it does more than just slow things down.
That covers dermatophytes — ringworm, jock itch, athlete's foot — and Candida, the yeast behind most skin-fold rashes. Miconazole also has modest activity against some gram-positive bacteria. That matters more than it sounds: the sore, soggy, smelly skin between the toes is usually fungus plus bacteria together, and a cream that hits both often settles it when a pure antifungal does not.
Steroid creams on the same rash without advice. They ease the itch and let the fungus spread.
Applying it to skin that is still damp. In a fold, that undoes most of the benefit of the powder.
Untreated shoes and socks. Spray or powder the insides of your shoes while you treat your feet.
Latex condoms and diaphragms for 72 hours after using the vaginal cream or ovules — the base weakens latex. The skin products do not affect latex.
Warfarin, if you are using the vaginal or oral forms. Miconazole absorbed from those routes can raise the INR enough to cause bleeding, and it is a well-documented interaction that catches people out because the product is sold over the counter. Tell whoever manages your warfarin. The skin cream and powder are not a concern — almost none of it gets into the body.
Days two to four
Itch and burning settle. The rash still needs treating.
Weeks one to two
Redness and scaling fade. Ringworm and jock itch usually look clear around now.
Weeks two to four
Athlete's foot needs the longer end. The soggy skin between the toes firms up first; the dry, scaly kind on the sole is the slowest to go.
No change by two weeks
Worth reconsidering the diagnosis, or switching to terbinafine, rather than continuing for another month.
Afterwards
Lighter or darker marks can linger for weeks where the rash was, and they show up more on brown and Black skin. That is pigment settling, not remaining infection.
Nothing rebounds and there is nothing to taper — you simply stop at the end of the course.
What happens next depends on why you had it. Ringworm treated fully usually stays away. Athlete's foot comes back often, because feet keep getting warm and damp inside shoes and because the shoes themselves hold the fungus. Many people keep using an antifungal powder a couple of times a week for that reason.
A rash in a skin fold will return whenever the fold gets damp again, no matter how well the yeast was treated. Drying, airflow and a barrier cream do more to prevent that than any antifungal.