How should you wait for results from a cream before deciding it doesn't work?

Yes, it depends on the cream and what it's for.


Let's just talk on average :)





Say for a rash, acne, pimple, or something of the sort. Something simple.How should you wait for results from a cream before deciding it doesn't work?
And I'm going to counter with...


It depends on the cream





Hydrocortisone for a rash? 20 minutes


Urea for Callouses? A couple days


Retin A for Acne? 6 weeks.





Depends on the active ingredient and how it effects the skin.