You treat it. It goes. You stop. It comes back.
That is not the shampoo failing. That is how dandruff works.
What dandruff actually is
A yeast called Malassezia lives on nearly everyone’s scalp. It is normal.
In some people it feeds on scalp oil and produces oleic acid as a byproduct. If your skin is sensitive to that, it inflames, speeds up skin cell turnover, and those cells shed in visible clumps.
So dandruff is not poor hygiene. It is an inflammatory response to something already living on your head.
Why it returns
Anti-dandruff shampoos control the yeast. They do not remove it, because you cannot remove it.
Stop treating, the yeast returns to previous levels, inflammation restarts, flaking comes back. Usually within two to four weeks.
The mistakes that keep it going
Rinsing straight away. Zinc pyrithione and ketoconazole need three to five minutes of contact. Wash-and-rinse does almost nothing.
Washing less because you think washing causes it. The opposite. Oil feeds the yeast.
Scratching with your nails. Tears the scalp, worsens inflammation, more flaking.
Stopping the moment it clears. The most common mistake by far. Drop to maintenance, do not stop.
What actually works
Treat three to four times a week until it settles. Then keep going twice a week indefinitely.
Rotate actives if one stops working. Zinc pyrithione, ketoconazole and selenium sulphide all work differently, and yeast can adapt.
Leave it on. Set a timer if you have to.
When to see a doctor
Get medical advice if the scalp is bleeding, weeping or painful, if there are thick scaly plaques, if patches spread to your face or chest, or if nothing improves after a month of correct use. That may be seborrhoeic dermatitis or psoriasis, which need different treatment.
