Heat styling

Ask any dermatologist or stylist what a surefire way to ruin your hair is and they will probably say heat-styling. Heat causes a number of problems: It lifts those tightly fitting tiles that create the cuticle layer, causing small spaces where water and other substances can enter and cause damage. Heat can also damage and remove small chips of the cuticle layer, causing a porous, hole-pocked surface that leaves hair weakened and prone to splitting, fraying, and breaking.

Research has found that blow-dryers operating at over 340 degre F (175 degre C) and curling irons, straightening irons, and hot rollers that reach over 250 degre F (125 degre C) cause splittin and fraying of the hair shaft.

The best way to avoid heat damage is to air-dry hair and stay away from heated curling and straightening appliances. "But my hair looks terrible if I don't blow­dry," you say. First, try talking to your hairdresser about a style that looks fabulous when dried naturally. If you don't settle on an acceptable style, try and stick to the following rules: Blow-dry only when necessary (for example, when you're going out), prep hair with a leave-in conditioner for a bit of protection, and hold the blower at least 6 inches (15 cm) from the head.

As for the curling irons, straightening irons, and hot rollers, find a style that works with your natural texture and you won't need to fuss with these things again.

If you habitually twirl your hair, you're weakening your strands, and this could lead to splitting and breakage.

Over-processing with chemical treatments

Anything that temporarily or permanently changes the structure of your hair can damage strands. Hair colors, permanent waves, and chemical straightening treatments qualify as strand-wreckers. How much damage a chemical process causes depends on the process. For instance, semi­permanent hair color, which washes out in several shampoos, dries out hair, and lightly roughs up the cuticle. It isn't as injurious as hair bleach, which breaks open the cuticle and bleaches hair's natural pigment to create colorless strands. Similarly, a treatment designed to loosen a person's natural curls won't alter hair as much as a severe straightening service.