What is the ruling on applying minoxidil gel to the head without knowing its source and purity, and what is the ruling on prayer when it is applied?

Minoxidil is permissible if it is free of impure, unlawful, or harmful substances. If it is applied after ablution (wudu'), the prayer is valid. However, if it is applied before ablution, it might form a layer that prevents water from reaching the hair, which would invalidate the ablution, as wiping over the head is an obligatory part of it. Therefore, it must be removed before ablution to ensure water directly reaches the hair.