Hair straightening is a hair styling technique used since the 1890s involving the flattening and straightening of hair in order to give it a smooth, streamlined, and sleek appearance. … If done often, flat irons andStraightening irons. Straightening irons, straighteners, or flat irons work by breaking down the positive hydrogen bonds found in the hair’s cortex, which cause hair to open, bend and become curly. … Heated metal implements slide more easily through the hair, reducing damage and dryness. chemicals can be damaging to hair.