For a decade now, Hollywood acting has been slowly, steadily poisoned by a bacterium called Clostridium botulinum. This week, I was watching the hypnotically horrible new Coen brothers movie, No Country For Old Men, and I couldn't shake off the sense there was something different, something thrilling and vivid, about the performances of all the lead actors: Tommy Lee Jones, Javier Bardem and Josh Brolin. It was only after half an hour of awe that I realised what it was. They can all move their faces.

Today, most actors in most movies have deliberately paralysed faces, incapable of registering anything. An ocean of Botox and collagen has been jabbed into the most famous faces on earth – leaving the audience feeling disconnected without knowing why.

Yet in this movie, the lines and crevices on the forehead of Tommy Lee Jones are as rugged as the Texas desert his sheriff character patrols. With imperceptibly tiny movements of these crags of skin, he can convey pain and panic and grief. Similarly, Javier Bardem's portrait of a blank-eyed psychopath works precisely because we can see that his sagging face is capable of more than blankness.

The majority of Hollywood stars are simply incapable of doing this. I don't just mean people like Melanie Griffiths, who have been left looking like Salvador Dali nightmare scenes; I mean the top-of-the-billing big stars who are still revered as greats. I'm thinking of one famous actress who claims that her face remains unlined because of the care she takes in looking after it. A decade ago, she was an impish, clever performer skipping towards greatness. Today, she has been jabbed and stabbed into a simulacrum of perfection – so her face can do nothing. It cannot register pleasure or pain; it can only remain in a frozen rictus, fitting for a performance in high-end adverts and no more.

Almost every American movie I see now contains a cast in the same poisoned state. Sure, Hollywood actresses have always altered their appearances: in the 1930s, several starlets swallowed tapeworm eggs to lose weight. But the procedures of the Nineties and Noughties are more disabling, in acting terms, than those of the past. In the 1940s, Rita Hayworth had a few minor cosmetic procedures: she had electrolysis on her hairline to give her a more exaggerated widow's peak. (The studio though it made her look "more exotic".) Marilyn Monroe had work on her chin-line. But they didn't do anything that would alter their abilities to move their faces – and act.

Botox is much more extreme for an actor. It doesn't just tighten or alter skin; it paralyses nerves. In Sarah Churchwell's brilliant book The Many Lives of Marilyn Monroe, there is a small story that shows how important the tiny, almost unreadable facial signals rendered impossible by Botox are to big screen acting. In the 1956 movie Bus Stop, Marilyn was cast opposite Don Murray, a much-garlanded stage actor breaking into the movies for the first time. When he shot scenes with her, he concluded that she was a dead, dismal actress, because she didn't seem to be doing anything in their scenes but standing there limply. Later, Dame Sybil Thorndike had exactly the same reaction.

But when they saw the rushes, they realised Marilyn was the only one among them who knew how to act for the camera: she had tiny, toned-down facial responses that were sure to melt the boy in the 22nd row.

If Marilyn had been Botoxed, she would have been turned into precisely the clothes-shop dummy Murray and Thorndike thought she was. Collagen is just as bad: if a face has puffed-up, immobile lips, its capacity for basic expression is largely gone. This is, I'm sure, one reason why British actresses have been doing so well at the Oscars for the past 10 years: they haven't been facially paralysed. Helen Mirren, Judi Dench and – this year, in the achingly sad Away From Her – Julie Christie have accepted the potential richness that comes from worry-lines and crows' feet. They use them. They know they suggest depth and richness and life.

Of course, this Botox-bind leaves actresses who are hitting the Hollywood-elderly of 40 in a cruel position. If they refuse to have the face done, they can't get cast. But if they have the face done, they can't act. They are trapped by our creepy desire to have any sign of ageing banished from our sight-lines, even on the cinema screen.

Alfred Hitchcock once said, "The greatest special effect is a close-up of the human face." Botox has stripped this effect from the movies – and left our films frozen.

j.hari@independent.co.uk