Severe Combined Immunodeficiency (SCID) is a real thing. The teen romance “Everything, Everything,” about a girl with SCID who can’t leave her house for fear of dying from a common cold — it’s like being allergic to everything, she says — is not.

Inside her hermetically sealed Los Angeles mansion, which includes an airlock, a machine for irradiating her wardrobe of plain white T-shirts and a sanitizing bathtub, Maddy (Amandla Stenberg) lives with her widowed mother (Anika Noni Rose), who is, conveniently, a physician. Although Mom’s specialization is never mentioned, she must be a celebrity plastic surgeon to afford this germaphobe-in-outer-space setup, which includes a full-time nurse/chef (Ana de la Reguera) and high-tech appliances controlled by Amazon Echo.

Maddy, who hasn’t left the house in 17 years, is remarkably poised, articulate, well-adjusted and smart — a poster child for, presumably, home schooling who, having just turned 18, whiles away her time by reading, drawing, writing sassy, haikulike classic-movie reviews on her personal website and taking online architecture classes, for which she builds surprisingly accomplished scale models, all of which include a small astronaut figurine.

Into this already too-perfect scenario comes a Cute Boy Next Door: Olly (Nick Robinson), who immediately strikes up a texting relationship with Maddy after they briefly lock eyes from their bedroom windows. In short order, they are exchanging flirty banter — or what passes for such, in the cloyingly arch screenplay by J. Mills Goodloe, based on Nicola Yoon’s 2015 YA novel.

The seal on Maddy’s autoclaved world can’t withstand the pressure of such swelling adolescent hormones and soon Maddy and Olly are meeting for chastely unrequited face time.

More experienced viewers probably will, for their part, spot the movie’s downbeat twists from a mile away. No amount of mental preparation, however, can vaccinate you against the one plot development that should, emphatically, not happen, but does.

Stenberg and Robinson are enormously appealing young actors, but charisma only goes so far in a story that manages to be sterile and wildly far-fetched.