Anti-Dandruff Shampoos: What Zinc Pyrithione and Ketoconazole Actually Do

Dandruff (and its more inflamed cousin, seborrheic dermatitis) is most commonly linked to an overgrowth of Malassezia, a yeast that lives naturally on most people’s scalps but can cause flaking and irritation when it overproliferates, often combined with excess oil and individual scalp sensitivity. Understanding this changes how you should actually use an anti-dandruff shampoo.

Zinc pyrithione is antifungal and antibacterial, and is one of the most common actives in over-the-counter anti-dandruff shampoos. It works by reducing the yeast population on the scalp.

Ketoconazole (found in some over-the-counter formulas, and in stronger prescription concentrations) is a more targeted antifungal, generally considered effective at lower usage frequency than zinc pyrithione for the same effect, though this can vary by individual and severity.

Selenium sulfide and coal tar are other common actives — selenium sulfide is antifungal and slows skin cell turnover; coal tar slows skin cell turnover and has anti-inflammatory effects, though it carries a distinctive smell some people prefer to avoid.

The detail most people get wrong: contact time matters more than most people give it credit for. These actives generally need a few minutes on the scalp to work, not a quick lather-and-rinse. A common approach is leaving the shampoo on the scalp for 3–5 minutes before rinsing, and it’s also common to alternate an anti-dandruff shampoo with a regular one rather than using it for every wash, both to manage scalp dryness from the actives and because effectiveness can plateau with constant use of the same active. If over-the-counter options aren’t controlling it after several weeks of consistent, correct use, that’s the point to see a dermatologist rather than escalating to stronger and stronger drugstore formulas on your own.