Straightening hair...

[x-Dahlia-x]

I've already posted this but it appears not to have been put on the site so I'll do it again:

Recently whenever I straighten my hair it gets V. greasy, especially at the back. My hair was completely clean beforehand as I'd just washed it. My sister has the same straighteners and it doesn't do this to her hair but her hair is wavy and mine is mostly straight with kinks at the end. Can anyone shed any light because I'd like to straighten it at the weekend because I'm going out but I'm scared it will go all greasy & horrible! Help!

P.S My straighteners arn't cheap rubbish ones, they are a decent make and are pure cermaic, not ceramic coated and my hair never did this when I first got them.