Kim Kardashian West doesn't smile ''because it causes wrinkles''.

The 34-year-old television personality often looks serious in photographs and avoids exposing her teeth when posing, explaining she does so because she doesn't want such expressions causing lines on her face.

Captioning a rare photo of her laughing with pal Shamari Maurice on Instagram, she wrote: ''See I do smile... even laugh on occasion. Not too often though because it causes wrinkles (sic).''

The 'Keeping Up With the Kardashians' star - who has 18-month-old daughter North West with her husband, Kanye West, 37 - has made her fear of developing a furrowed brow known in the past, having a facial of her own blood on an old episode of the reality show which aired last year.

In the clip, the socialite was seen having blood drawn from her arm, before it was splattered onto her face using acupuncture needles.

Before trying the strange technique, she said: ''I love trying anything that makes you look and feel youthful.''

However, the businesswoman vowed to stay away from cosmetic surgery following the procedure, which indicates why she may be so keen to avoid developing laughter lines.

She said: ''I will never get a facelift if it feels like that.''