The phrase "are often extreme" is correct and usable in written English.
It can be used to describe situations, opinions, or behaviors that tend to be very intense or severe.
Example: "The reactions to the news are often extreme, ranging from joy to outrage."
Alternatives: "tend to be extreme" or "frequently are extreme".
Pollution levels are often extreme.
The study found that the socioeconomic differences among residents are often extreme.
David Alden's staging turns Donizetti's most popular work into an examination of Victorian psychopathology, and the results are often extreme.
Worse, when paternity leave is offered, the pressures on men not to take it are often extreme.
Neurological disabilities may include severely disabling attributes in many people, but are often extreme manifestations of traits existing in the general population.
However, the affects are often extreme and unpredictable because they contain one or a number of unknown or newly invented chemicals about which little is known.
He was often extreme in his nationalism.
But just as Jones's work is often extreme and unpredictable, so is the critical response to it.
Davey admitted that the sixth and latest season was "pretty intense" but said that Sky had only received three complaints about the show's often extreme scenes of sex and violence.
She spoke of contact between dancers in partnering — noting briefly that amid "abstract" dancing contact allows for more specific meaning — then had two show a duet where contact was often extreme, with one dancer clinging onto and clambering over another.
The violence is often extreme – the Jewish Nazi hunters have a habit of scalping their victims; one hunter likes to batter in his antagonist's head with a baseball bat; and a shoot-out in an underground bar is sheer bloody carnage – but it comes in bursts and has a comic book element about it.
