Tanya L Chartrand is a professor of psychology and neuroscience at the Duke University Fuqua School of Business in North Carolina. With David T Neal from the University of Southern California she recently published a paper entitled "Embodied Emotion Perception: Amplifying and Dampening Facial Feedback Modulates Emotional Perception Accuracy", which found that using Botox – a neurotoxin injected into muscles to reduce frown lines – reduces a person's ability to empathise with others.

It wouldn't surprise people to hear that it's difficult to tell what the Botoxed are feeling, but your study found that the Botoxed have little idea what we are feeling?

Yes, we always assume that you can't tell what the Botoxed people are feeling because their faces are somewhat paralyzed and can appear frozen, but what is less intuitive is that being injected with Botox impairs their ability to understand what other people around you are feeling.

To demonstrate this you asked women to look at photographs of people's eyes and match them to human emotions…

Yes, it's called the "Reading the mind in the eyes test", and it's sometimes given to people on the autism spectrum. The people who had a Botox treatment in the previous two weeks were not as accurate as our control group, who had been treated with Restylane – a skin filler – whose results were similar to untreated adults.

Why did you choose a control group who had used filler, rather than a random group?

We wanted to match the two groups on everything we could except that one had the paralysing agent and the other hadn't. The Restylane group are demographically similar to the Botox group – in terms of age and gender, socio-economic status, and had the same concerns with looking good. So if we got a random group of people who would never have one of these cosmetic procedures then they could differ in a lot of other ways. This way we made sure that we were just isolating the fact that Botox is the cause.

The study talks about "embodied cognition" – could you explain?

This is the idea that the way we think and feel is grounded in our bodies. The way we understand others' emotions is to experience those emotions ourselves. We do this with facial micro-mimicry. So if you are wincing in pain I immediately do a micro-wince, and that sends signals to my brain that this person is experiencing pain, and by experiencing it myself I now understand what you are going through.

So Botox messes with our embodied cognition?

Yes, it's interfering with that first step, which is mimicking facial expressions and that's what sets the whole thing off. If you can't mimic someone's wince, your brain isn't going to be sent the same message – that this person is experiencing pain – so you end up not being as accurate and not really understanding the emotion.

If your empathy skills are inhibited by Botox what outcomes might that have for your day-to-day life?

My collaborator, David Neal, was initially interested in looking at the consequences for romantic relationships. Say if you're married, you get Botox and then if you are not able to understand what your partner is feeling any more, it could lead to romantic dissatisfaction. We needed to see the basic effect before looking at some downstream consequences for marital satisfaction. This is maybe what we will study next.

So someone could have Botox to look better, say for going on dates, but then they find there's no "connection"…

Absolutely. The irony is that having Botox to look better and be more attractive may make you less attractive in some ways, because you're not empathising with others so well.

So are the benefits of Botox overrated?

I know there's been some research showing that Botox can help people who are depressed feel better. So I wouldn't want to say there aren't some positive benefits people gain from feeling better about themselves, feeling more attractive, feeling younger, but this is one negative to point out to people. Some people will think, "Fine, I'd rather not empathise." It's not like Botox makes you completely unable to understand any emotions in others, but it definitely reduces your capacity to understand those emotions.

The idea for the study came from a paper that said long and happily married couples began to resemble each other, didn't it?

Yes, there is some research that shows that. When you look at side-by-side photos of couples, you see that people who have been happily married for 25 years or so look alike. The theory is that if they have been mimicking each other's facial expressions for 25 years they start to form the same wrinkles, have the same expressions and so on.

Would you use Botox yourself?

Knowing what my own research has uncovered I would not. Recently I was talking to a woman of 22 who was doing it "preventively" – the latest thing is that women are told they should be doing it now so they don't form wrinkles in their 30s and 40s – she was shocked that I don't do it. Eventually I think I'm going to be a lone woman standing.