Cindy Crawford thinks the expectations of the fashion industry are "overwhelming".
The 49-year-old supermodel admits she finds it tough ageing, having relied on her looks for her job.
She said: "Having been a model now for more than 30 years and dependent on my looks for my work, seeing those changes [as I age] might even be a little bit harder for me.
"At times the pressure to live up to the fashion industry's expectations feels overwhelming. I can still pull off a miniskirt and 5 inch heels on set - but probably not in real life."
However, Cindy also insists it is only her "real life" persona that is ageing as her modelling one is part of an "illusion".
Writing in an extract from her autobiography 'Becoming by Cindy Crawford' as printed in The Sunday Times' Style magazine, she added: "Sometimes I forget that the images I am used to seeing of myself aren't real, that they are all part of the illusion of being Cindy Crawford.
"And then I will catch a glimpse of the real, unretouched Cindy or see an unflattering paparazzi shot, and it's a shocker."