Heat from flat irons close to the scalp can damage its moisture barrier, allowing moisture to escape.
This in turn can cause the scalp to become dry and flaky.
Dryness is one of the major symptoms of dandruff. By exacerbating that, hair straighteners can also make a dandruff problem appear worse.
Add to that the itching associated with the irritation, you can actually do more damage to the scalp.
How to straighten the right way
In order to keep your hair and scalp healthy when straightening it, there are a few things to keep in mind:
Keep the flat iron on a lower setting. Hair becomes damaged above 350 Fahrenheit (180°C), so keeping the temperature around this point will minimize the harm
Straighten your hair only when it’s dry, as wet hair is more easily damaged at lower temperatures
Be gentle when straightening your hair, so that you do not pull it unnecessarily
Use a good conditioner to help the flat iron slide more easily down your hair strands without damaging them.