It is two drugs doing two different jobs to the same wart.
Salicylic acid is a keratolytic — it dissolves the protein bonds holding dead skin cells together. On a wart, that thick horny cap is both armor and the bulk of the problem. Softening and shedding it thins the lesion and lets anything else get in. Salicylic acid on its own, used patiently, is the best-evidenced home wart treatment there is.
5-fluorouracil is an antimetabolite. Cells that are dividing rapidly take it up in place of a normal DNA building block and then cannot finish copying themselves. Wart tissue is infected skin driven into fast division by human papillomavirus, so it is exactly the kind of tissue that is vulnerable.
The third element is the vehicle. The gel is designed to be adhesive and slow-releasing, so the drug stays on a small wart overnight instead of wiping off on a sock. Combined with tape occlusion, which softens the skin and drives the drug in, that is the actual point of difference from painting on separate products.
Neither ingredient kills the virus directly. Both remove the tissue the virus lives in, and the irritation involved sometimes wakes the immune system up to the infection — which is what ultimately clears a wart for good.
The wart usually starts to look whiter, softer and flatter within the first couple of weeks. That is the salicylic acid doing its part, and it is not the same as clearance.
Real clearance takes longer. Warts on the hands and around the nails often respond over several weeks. Plantar warts on the sole, which are thick and under constant pressure, can take a few months and do not always clear at all.
The skin telling you it has worked is the return of normal fingerprint lines or skin ridges across the surface. A wart destroys those lines; a healed patch of skin gets them back. Black dots and a distinct border mean there is wart left.
If nothing has changed by the point your prescriber set for review, it is time to switch rather than to keep going. Warts have a long list of other options — cryotherapy, candida antigen injection, bleomycin injection, curettage and electrosurgery — and no single one wins for everybody.
If the wart cleared, stopping is the end of it. Warts that are genuinely gone — normal skin lines, no black dots — usually stay gone at that site.
If the wart was only partly treated, it typically thickens back up over the following weeks. Warts do not hold a partial result well.
Some warts come back after apparently clearing, because the virus persists in nearby skin. That is not a failure of this particular product; it happens with every wart treatment there is.
Untreated warts are harmless in the medical sense. Most clear by themselves eventually, often within a couple of years, and doing nothing is a legitimate option for a wart that is not painful, spreading or bothering you.