Em dashes are not the problem. Stacked em dashes are.

The idea did not come from a study. It came from a fashion podcast clip in March 2025, about a brand’s rebranding post, which coined the phrase “the ChatGPT hyphen” and travelled from there. By November it had reached national radio, complete with a counter-movement of writers defending a mark they had used for years.

The Associated Press wrote about it in August 2025 and was blunt: the em dash “has been around for many years. In fact, they are so ubiquitous in AP lingo, we just call them dashes.” On the question everyone actually wants answered, the Stylebook is equally direct — “AP does not have a limit on using long dashes” — while adding, reasonably, that many writers overuse them and that a comma, a semicolon or a new sentence often does the job.

What the manuals actually say

Chicago sets no number either. It calls the em dash the most versatile of the dashes and treats the choice between dashes, commas, parentheses and a colon as a matter of effect. Its editors have said in as many words that overuse is a matter of taste and of the writer’s ear.

There is exactly one hard rule, and it is structural rather than numerical: “the em dash should never be used within or immediately following another element set off by an em dash (or pair of em dashes). Use parentheses or commas instead.” That is the rule this article is named after. Not too many dashes — dashes inside dashes, where the reader loses track of which aside they are in.

Spacing is not settled either, and it does not split neatly by country. Chicago sets the em dash closed up, with no space on either side. AP, also American, spaces it on both sides. British practice generally uses a spaced en dash in its place. Three regimes, none of them wrong.

What the measurements show

Two attempts have been published, and they are worth reading together because they pull in opposite directions on the question that matters.

The first looked at nearly seventy thousand medRxiv preprints and asked whether the discussion section contained an em dash at all. Before late 2022 the answer was yes for about four per cent of them; afterwards, for about twelve per cent, with the figure reaching roughly twenty per cent in 2025. The rise is gradual rather than a step change, and it survives the author’s own falsification tests. The author states the limit of the result plainly: it is a population-level indicator, not a per-paper detector, and the design cannot establish cause.

The second counted em dashes per thousand words in published human essays and in the output of a dozen models. The human essays averaged about three per thousand words and ranged from a third of one to seventeen. The models ranged from zero to about eleven. The two ranges overlap completely: the most dash-heavy human writing in the sample exceeded every model measured, several models sat below the human average, and two used none at all.

That is the whole case against the advice. Density may well have shifted across a corpus. It does not identify a page, and editing your own page to sit under an imagined threshold is optimising against a measurement nobody can perform on it.

What deleting them all costs

Replacing every em dash with a hyphen is not a neutral swap, because the two characters carry different line-breaking behaviour. Unicode classes the em dash as a break opportunity before and after; the hyphen-minus allows a break after it only. Swap one for the other throughout and you have changed where a paragraph is allowed to wrap, which changes its justification and its rag.

Screen readers treat them differently too, though less dramatically than you might expect. In testing at default punctuation settings, JAWS announces “m dash” for the em dash and “dash” for the hyphen; NVDA says nothing for either; VoiceOver pauses briefly without naming either one. So the substitution changes what one reader in three hears, and is inaudible to the others.

• Keep the dash when it marks a genuine break in thought. That is the job it does better than a comma.
• Never nest one aside inside another. That is the rule Chicago actually gives, and it is the one that makes a sentence hard to follow.
• If a paragraph has several, ask whether a semicolon or a full stop would carry the same turn. Often it would, and the prose gets firmer.
• Do not run a find-and-replace across a finished document to lower a number. You will change its typography to satisfy a test that cannot be run on it.