To get all that steamy action onto the screen, Hollywood has to engage in some decidedly unsexy shenanigans. Suffice it to say that on a major production, everything that can be simulated is simulated. Many actors simply refuse to do even simulated sex scenes, or if they do, they have strict rules in their contract stating what degree of nudity and / or acts they will do or even be portrayed as doing. Some actors, of course, are totally fine with “anything goes.” For performers who don’t mind being portrayed as having sex but won’t do it themselves, a body double with CGI editing is used.
Most anything you can’t see on camera is covered, even if they have to do it with a pastie (modern crews call them “modesty patches”). When two characters appear to be engaged in penetration, chances are there’s a pillow hidden between them. The set is usually closed with minimal staff around to help the actors feel comfortable. Indeed, more than one performer has indulged in a sip of alcohol to help feel looser.
Outside the frame of the finished shot, you’d barely recognize the atmosphere. Chances are that the sex is tightly choreographed, sometimes even by a dance choreographer, who outlines each movement. Where the exact details aren’t important, actors can improvise. The performers typically keep it light, using some humor to defuse the tension. Make-up artists will apply make-up to the actor’s whole body, and likely spray down the actors with baby oil to give them that sweaty look. Waiting just out of camera range is an assistant with a robe or blanket to cover the performers between shots.
By the way, all this technical complication sometimes doesn’t damper the flame! Many an actor couple in real life has started out portraying lovers onscreen, such as the case with Adam Sandler and Drew Barrymore, Julia Roberts and Richard Gere, and Angelina Jolie and Brad Pitt. Apparently having good chemistry onscreen sometimes sparks the romantic flame, so maybe there’s a bit of reality to that Hollywood magic after all.