Amanda Seyfried refuses to undergo Botox because of a lack of research into its potential side-effects, despite acquaintances often insisting she needs the treatment.
The Mamma Mia! star, 25, admits she is already conscious of the small changes to her face as she ages because of the pressure on women in Hollywood to look young.
And although tactless pals urge her to invest in face-freezing injections, the actress doesn't trust the lack of evidence into the potential dangers of Botox use over several years.
She tells Britain's Glamour magazine, "Living in a society where there's so much attention given to age-defying products, I'm really aware of how my face is changing, even at my age... because once you start, I don't think you can stop.
"A good friend recently told me that I really had to whiten my teeth and I thought to myself, 'That's not wrong', but people I don't know so well have told me I need Botox, and those people I've ignored because although it's accepted now, the research isn't there yet."