Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Get emergency help if a medicine causes trouble breathing, swelling of the face or throat, faintness, or a widespread blistering or peeling rash.
These can be signs of a serious medication reaction.
And for anyone, someone who:
Seek prompt medical assessment if the skin becomes painful, hot, swollen, blistered, or starts draining pus, or if you develop a fever.
These symptoms are not typical of tinea versicolor and may have another cause.
Arrange a routine appointment if this is your first episode and you are unsure what is causing the patches.
You should also seek routine medical advice if the rash is widespread, keeps returning, or does not improve after an antifungal product has been used as directed.
The article also says
Ask a healthcare professional before taking oral antifungal medicine.
This is particularly important if you are pregnant or breastfeeding, have liver problems, or take other medicines that could interact with it.
Tinea versicolor itself is not an emergency.
Every sign above is quoted from the sofidex article on Tinea versicolor. If you are not sure, err upward — it is always reasonable to be checked.