Most Amazon PPC attention goes toward getting more of the right clicks. Negative keywords do the opposite job — stopping the wrong ones — and they’re easy to under-use simply because they don’t show up as a positive number anywhere in the dashboard.
What a negative keyword actually does
A negative keyword tells Amazon not to show your ad for a specific search term, even if that term would otherwise match one of your active keywords or Auto targeting. It doesn’t add reach; it removes irrelevant reach that was costing money without converting.
Where they come from
The clearest source is your own Search Term Report: any search term with meaningful clicks and zero orders is a direct candidate. Broad and Phrase match campaigns generate this kind of data constantly — the wider net that makes them useful for discovery is the same thing that guarantees some irrelevant matches.
Two rules worth getting right
There’s no shared negative list on Amazon. A term added as a negative in one campaign has no effect on any other campaign — it has to be added everywhere it’s actually a problem, individually.
Never negative a keyword that’s converting. This sounds obvious, but it’s a common mistake when someone sees a high ACoS on a term and reaches straight for “negative” instead of “reduce the bid.” A converting keyword with a high ACoS is a bidding problem, not a relevance problem — negating it removes sales, not waste. Reducing the bid gradually addresses the actual issue without losing the order volume.
Where negatives connect to campaign structure
Negative keywords are also the mechanism that makes the tiered funnel work: every time a search term gets promoted from Auto to Phrase, or Phrase to Exact, it gets added as a Negative Exact in the campaign it came from — otherwise the old and new campaigns end up bidding against each other for the exact same search.
Reviewed regularly, negative keywords are one of the few PPC levers that only ever save money, never cost it — which makes them one of the easiest wins to leave sitting in a report nobody checked this week.