Straighten Fine Hair
Are there any special precautions to take since my hair is much weaker than my friend's thick hair?
A: Yes, actually. You can feel confident about straightening your hair, as long as you do it properly.
You will also want to be sure to use lower heat settings on the iron itself, with your fine hair. Because the hair is fine (smaller in diameter) you don't need as much heat to penetrate all the way through the hair. Using the same heat setting as your friend with coarser hair will only risk burning your finer hair.
Finally, you want to pass the iron through your hair quickly in even, smooth passes. The goal is to never let the iron's heating-plates rest on one area of the hair for more than a second or two at most. By passing the iron through the hair with even tension, you help to smooth the waves and bends in the hair and create that sleek, shiny finish you desire.
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See also:
How to treat fine hair
How often you can use hair straighteners
How badly will straightening damage my hair?
How often should I use heat protectant when I flat iron my hair?