What effect does heat have on the hair structure?

If used to much or too often, heat can damage your by frying it and making it look ratty. Also heat can create slipt ends. Someone I know has actually lost hair because they straightend their hair almost everyday for almost a year. They had to buy extensions, not because they wanted longer hair, but because they needed these to make it look like they had more than a little hair. Some people don't even realize it, but blow-drying your hair can also be very damaging. Try letting your hair dry naturally ocasionally. You will be pleased. Beware that heat isn't the only way to kill your hair. Dying your hair is also dangerous. Anything harmful to your hair can permanatly ruin your hair and make it harder or impossible to grow any back. BE CAREFUL.

I hope this helps:)