Dandruff is caused by fungus? wow.
How would taking anti fungal pills systemically kill the fungus that is growing in the dead skin cells? Maybe I should just apply an anti fungal like selenium selsun blue and keep it on my head for half and hour for a week until most of that fungus is killed off.
The fungus is not growing in the dead skin. Its Killing the skin its growing into.
The trouble with fungi is that the real core of the fungus is the Mycelium - tiny fibrils they send out into surrounding tissue.
Topical treatments can never kill ALL of the mycelia in the tissue, just knock it back some... the symptoms seems to stop, but the mycelium is growing back...and keeps penetrating new skin tissue.
Newer anitfungal PILLS work by saturating your TISSUES with a compound toxic to fungi.
Thus topical agents are like a herbicide that kills weeds by soaking into them from without...
Whereas the systemic anitfungals are like Poisoning the ground in which the weed grow.
As to topical dandruff treatments... actually, what a lot of people don't get is that you are SUPPOSED to leave them on the scalp for 10 minutes or so...
But still... no topical treatment known will actually eradicate the underlying fungal infection.
Dandruff shampoos, like athelete's foot sprays, are something you have to keep using continuously to manage a chronic infection.