Styling with high heat is never good for the hair, but you can prevent damage to your hair, by using some good heat protection products.
There is a simple rule for the best result: If your are styling your hair with a straightener or curling iron always use alcohol based products. Normally you would think that alcohol dries out the hair, but when you use heating tools, it’s the opposite way. Scientist have found out that water will damage your hair even more when you are styling your hair with heat. The less water, the smaller damage. That’s why alcohol based products is good for the hair: It makes the water evaporate from the hair.
My advise: Stay away from water based product, and use alcohol based products for styling with heat. If you only blow dry your hair with middle temperature I would recommend styling products based on water.
Never style your hair with heat when it’s wet.