Look at almost any of our kits and you will find the same pattern: a drop that is taken with water, and an ointment or spray that goes on the affected area.
Two routes, one routine
The drop is the internal part of the routine. The ointment or spray works locally, on the skin or the area itself. They are formulated as a pair and are meant to run for the same course length.
Can you buy just one?
Yes — several items are sold separately, and some people start with one before ordering the kit. The kit exists because the two are designed to be used together, and it costs less than buying the items one at a time.