Kylie Jenner. Picture: Reuters

Kylie Jenner had lip fillers after being criticised by the first guy she kissed for her small pout.

The 20-year-old reality star admitted she had her mouth injected to make it plumper because she felt so "insecure" from the cruel teenage comments.

Speaking to a therapist in a scene from the latest episode of her E! show 'Life of Kylie', she said: "I was 15 and I was insecure about my lips. I have really small lips. And it was like one of my first kisses and a guy was like, 'I didn't think you would be a good kisser because you have such small lips.' 

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"But I took that really hard. Just when a guy you like says that, I don't know, it just really affected me. I just didn't feel desirable or pretty. 

"I really wanted bigger lips. I would overline my lips with lip liner just to create the illusion of bigger lips. And then finally I was like this lip liner isn't doing it. [I] ended up getting my lips done."

Despite having the lip procedure at a young age, Kylie insists she's in no hurry to grow up and she's happy to make "bad decisions" and mistakes in the spotlight.

She said: "I'm trying to not grow up too fast. I love my age. I love my fans. I love that we're all young -- the new generation. I want to make mistakes. I want to make bad decisions and learn from them. That's the only way I'm going to grow."

The episode also saw the lip kit guru and her mother and manager, Kris Jenner, travel to Peru to see the work done by Smile Train - a charity providing corrective surgery for children with cleft lips and palates - and Kylie was amazed by the courage and confidence of the youngsters she met.

She said: "When I was younger, I definitely didn't have the best confidence at all. These kids have it on a whole other level. So Smile Train touched me and I felt the urge to get involved. 

"It's amazing to know that the money I'm donating is actually doing something, changing lives. 

"But it is heartbreaking to know that there are so many people who just don't have the resources....

"This experience really made me appreciate my family and our health."