The news that younger women than ever are resorting to Botox as a "preventive measure" has got me thinking about the time a few years ago when I went to stay with a friend. The face she greeted me with was not her face. One of her eyelids sagged, giving her a strange lopsided smile. Distress bubbled up inside me. Had she been struck down with Bell's palsy? Had a stroke? Why didn't she tell me?

"What's happened to your face?" I blurted out, feeling the tears rise in my eyes.

"It's no big deal," she said, brushing me off with a wave of the hand. "It's just a bit of Botox gone wrong. It's not permanent or anything."

It took me a while to fully process her answer. My startlingly confident, formidably intelligent, beautiful 31-year-old friend was getting Botox? And Botox had caused her eye to sag as though she'd had a stroke? Of course, I knew film stars and celebrities forked out in order to have this paralysing poison injected into their faces, but it wasn't something I'd anticipated someone I actually know would do.

Fast forward a few years and Botox seems far more common. I have other friends with the tell-tale shiny foreheads, though I've never again encountered a droopy eye. Yet Botoxed faces all have something in common. A strange vacancy, a peculiar dullness. Despite the glimmering smoothness of the skin – the odd way that light reflects off an unlined surface – there's a kind of deadness around the eyes. All my Botoxed friends look faintly angry, with a touch of indifference. It's a particular expression, rarely found in an unneedled face, and it takes some getting used to.

Lately, I've found myself feeling uneasy after spending time with these shiny-faced friends. The sense of connectedness we've always shared seems impeded by their impenetrable faces. In short, I miss their micro-expressions. I feel cut off from them, and come away lonely and disturbed. I worry how these frozen faces serve them in other parts of their lives. How do their partners feel? What about their children?

I know why women feel they need Botox. I understand the pressure on us all to maintain a youthful appearance. The relentless bombardment of media images and meta-messages. Our invisibility once past a certain age. The very real ramifications of ageing as a woman in our culture. But I can't help wondering about the costs of Botox, and not just as far as one's wallet is concerned.

There's no argument that Botox paralyses facial muscles. That's how it works. It minimises micro-expressions, those brief, involuntary facial expressions that reveal our unconscious feeling of anger, happiness, disgust, embarrassment or pride. In a sense, communicating with someone who's had Botox is like communicating with a static image – much of the body language involved is silenced. Considering that body language, mostly consisting of facial expressions, makes up at least half of any message being communicated, this is a significant loss.

But this facial paralysis also inhibits the ability of the Botoxed to mimic the facial expressions of others, which is critical in the formation of empathy. Facial micro-mimicry is the major way we understand others' emotions. If you are wincing in pain I immediately do a micro-wince, which sends a message to my brain about what you are experiencing. By experiencing it myself I understand what you are going through. This suggests that not only do I find my Botoxed friends hard to read, but they are also hindered in their capacity to read me. An unfortunate feedback cycle. The possible implications of this are frightening.

There has been a study into the effects of Botox on the ability to empathise, but nothing that specifically addresses the impacts on friendship, or the mother-infant bond. The absence of discussion around the effect of Botox on mothering is troubling considering that a mother's display of emotions is how the infant learns to interact with the world. Psychologists have a method for testing infant distress at unresponsive faces called the "still face paradigm". Any alarm bells ringing?

Empathy is a cornerstone of our relationships, vital to both building and maintaining positive interactions with others. That many women are presenting themselves as a still image is disturbing and worthy of consideration. The poker face, by definition, doesn't express anything. With the proliferation of "selfies" and the focus on static representations of women's faces, are we forgetting how much of who we are is communicated through facial expressions? Are we, in some sense, choosing a form of silence far more insidious than women have ever known in the past? Who benefits from the silencing of women's faces? And what is the cost?