The use of concerning as an adjective meaning of concern has been decried by writers and usage authorities for being grating, for being nonstandard, and for sounding like a made-up word. But these complaints are not grounds for saying concerning is incorrect or is not a real word. The complaint about concerning having a grating sound is subjective; we can’t block a word from the language just because some people dislike its sound. The complaint about it being nonstandard is a few decades behind the times. And all words are invented, so the complaint about concerning sounding “made up” doesn’t really say anything.
There are countless precedents for the formation of the participial adjective concerning from the verb concern, among them several synonyms of concerning that are similarly formed. For example, no one questions upsetting, disturbing, distressing, or alarming. If we accept these words, we should accept that concerning is a legitimate word, even if we don’t like it.
Also, while it’s true that concerning has grown in prevalence over the last few decades, the word is not new. The OED lists examples of concerning used this way from as far back as the 17th century, and additional examples are easily found in Google searches of historical texts. We’ve found no explanation of its recent increase, but our guess is that synonyms like alarming and troubling are sometimes too extreme to accurately replace concerning, which has perhaps become gentler in modern usage.
One complaint against concerning does stand up: The word is also a preposition meaning in reference to or regarding, and the adjectival concerning can cause confusion when readers or listeners initially interpret it as the preposition. For instance, if you hear someone say, “His email was concerning,” you might at first expect something to come after concerning. This complaint isn’t a rock-solid case, though, as many words in English have multiple functions, but it’s a good reason for those inclined against the word to continue avoiding it.
Some very concerning and necessary Doctrines of Religion the Philosofers were wholly ignorant of. [Sixteen Sermons on Select Subjects, by Isaac Terry (1746)]
[Y]our long absence and having no provision, and all things dear has obliged me to spend a great dall of money which has been very concerning to me … [Analecta scotica, by James Maidment (1837)]
He said he decided reluctantly to sell … because they wouldn’t sell their shares to him and “a number of things have occurred in the past six months which were concerning to me.” [Schenectady Gazette (1987)]
”But each time we hear it, it’s surprising and rather shocking, specifically as it relates to cancer. It’s quite concerning.” [New York Times (1999)]
Ne’eman’s remarks should be concerning to “every citizen who cares about what happens in Israel in terms of its values and democracy.” [Jewish Telegraphic Agency (2009)]
Construction union Ucatt said the announcement was very concerning. [BBC (2012)]
Ms Gillard omitted one of the most concerning and disheartening statistics. [The Age (2012)]