You can’t hide from smell in Parasite. It’s oppressive. It clings to you, seeping into your skin. It is omnipresent and sinister. Beyond being a mere symbol of social status, the smell threatens to expose one’s identity and the dark secrets lurking beneath. How did Bong Joon-ho make undetectable scents so indispensable to his film?

The film, set in modern-day Seoul, depicts the down-on-their-luck, basement-dwelling Kim family as they inveigle their way into becoming servants for the affluent Park family. As the Kims begin ascending the social ladder, the lies they have engineered are threatened with exposure. Smell is central to this twist of fate.

In Parasite, social inequalities are explored not through money or codes of conduct. The word “poor” is never uttered. Instead, the Kims’ social standing is revealed through body odours and scents. A pivotal moment comes when the Parks’ young son, Da-song, comments quizzically to his parents that the new driver and housekeeper “smell the same”.

In Parasite, smell shifts its note. In an earlier scene, the Kims’ apartment is inadvertently fumigated by street cleaners. The stench is welcomed as a cleanser by Ki-taek (Song Kang-ho). But it becomes a barrier to the Kims’ social climbing, driving tension and posing a silent threat that could expose them. As Mr Park (Lee Sun-kyn) begins to notice these unsettling aromas, the audience also become hypersensitive to their presence. The Parks’ privileged position leaves them feeling entitled to dictate which smells “cross a line”. The audience is left stuck in the middle.

Watch a trailer for Parasite.

Smell ultimately shatters the Parks’ universe, while reminding the Kims that their new clothes and more generous earnings will somehow never be enough. Both families demonstrate how social standing and smell interact. Without hesitation the Kims wade through sewage water, impervious to the stench, to retrieve their few belongings in a flood. Conversely Mr Park is decisively hampered by a smell he finds distasteful, during his own life-threatening family emergency.

“These [are the] moments where the basic respect you have for another human being is being shattered,” Bong says. “Smell really reflects your life. It shows if you’re struggling. what kind of work you do. Even when you sense the smell of someone else, you don’t talk about it in the open, because it can be rude.” In another interview, he expanded: “By talking about different smells, the film puts the class issue under the microscope. Through smells, the film’s tension and suspense mount, which eventually makes a multi-layered foundation for the upcoming tragedy.”

Heavy-handed … Ben Whishaw in Perfume. Photograph: Snap Stills/Rex/Shutterstock

We are more accustomed to sultry representations of smell. In Park Chan-wook’s The Handmaiden, scents are spine-tinglingly sensual, driving the erotic film’s narrative. Conversely, the attempt to mesh smells and visuals in Perfume: The Story of a Murderer is so heavy handed it becomes one stale mess. Viewers are assaulted with visuals of the film’s serial killer rubbing his nose against objects or the camera laboriously lingering on rotting fish. More recently, Sam Mendes’ Bafta-winning 1917, set in the fetid trenches, should be redolent but ignores the issue. As Lance-Corporal Schofield’s (George MacKay) hand plunges into a corpse’s guts or he clambers over bloated dead bodies in the water, smell is of little interest.

In Parasite smell rouses rawer emotions: anger, distrust, discomfort and a dark sense of foreboding. Something closer to the raw truth. Bong layers rich visuals, but smell remains the film’s emotive core. He is well aware of how smell can evoke memories. While researching his previous film Okja, he spent time at a large slaughterhouse and said the smell was the hardest thing to forget; it prompted him to temporarily become a vegan. In The Host, a machine spraying a chemical substance to disperse protesters recalls the director’s time at campus, when riot police shot tear gas at students. Bong remembers: “It was a very traumatic smell. It’s impossible to describe: nauseating, stinging, hot … It’s strange, sometimes I smell it in my dreams.”

The vividness and potency of smell in Parasite is a key part of what makes the film’s so arresting. Bong notes how this might contribute to its overall appeal: “Its substance smells pungent and cruel. But in terms of style, it is sweet and enticing. Perhaps this is a very unusual and appealing bouquet.” Oscar would agree.