Box Office Bomb: Budget, $80 million. Box office, $38,345,494 (domestic), $98,376,292 (worldwide). The Rotten Tomatoes consensus accused Ivan Reitman of attempting to remake Ghostbusters (1984), and several critics panned it for its liberal usage of Toilet Humour and Squick regarding the enemy aliens. It got an animated continuation that same year, but said show ran for only one season. Reitman would not direct his next cinematic movie for five years.
Creator Backlash: Don Jakoby's original script was far more serious than the finished product, thanks to credited co-writers David Diamond and David Weissman. He wasn't happy about it.
According to some design sketches, the final form of the alien's evolution would've been a much more humanoid form. However, seeing how difficult it how to make this a realistic threat, instead they went with the giant cell.
The mall that features in the third act was, in reality, a ghost mall abandoned for several years. The production team added store fronts and set dressing to make it look fully functional.
According to Ivan Reitman on the commentary track, contrary to popular belief, the prominent feature of Head&Shoulders was not a case of product placement; P&G wasn't approached for placement, no money was paid for the appearance, and the bottles shown were acquired by the production.