I you’re like me and own a flat-iron, you probably use it too often and crank the heat up too high. According to trichologist Iain Sallis, you should never heat an iron up above 180 degrees Celsius (or 356 degrees Fahrenheit). Beyond that you can potentially damage your hair’s cuticle, making your hair rough and frizzy. Over-heating your hair can also lead to split ends and eventual breakage. Yikes!