There are several different causes of split ends, which occur when a strand splits in two at the bottom of the hair shaft. The ends of the hair are naturally more prone to damage due to their distance from the scalp; the longer a person’s hair, the more likely he or she is to experience split ends. Heat styling, bleaching, and coloring hair are some of the most common causes of split ends. Handling hair roughly, especially when it is wet, can also result in damage.
The scalp naturally produces oils meant to coat and protect the hair from damage. As hair becomes longer, the ends tend to come in contact with less of the oils produced by the scalp, leaving each strand weaker at the ends than it is closer to the head. Once the ends split even a little, they gradually continue to break up the hair shaft, resulting in noticeable damage that can only be treated by trimming off the split ends.
Styling the hair with heat tools such as blow dryers, flat irons, and curling irons is one of the most common causes of split ends. The high levels of heat can singe the ends of the hair, making them weak enough to break. While certain products, often sold as heat protectant sprays, can help to limit some of this damage, hair that is routinely subjected to the high temperatures of a blow dryer or hot styling tool will become damaged much more quickly than hair that is allowed to air dry.
Bleach, often used for highlights or to lighten naturally darker hair, is incredibly rough on the ends of the hair. The bleach permanently alters its structure, removing not only the color, but also the oils and proteins that make the hair able to withstand normal styling. Hair that has been bleached becomes brittle, and can split even during a simple brushing, especially if it is bleached often.
While not as damaging as bleach, coloring the hair is also a cause of split ends. As with bleaching, color alters the structure of the hair, although simple hair dye does not typically lift any color. The chemicals in the hair dye rely on the natural oils of the hair to limit damage; this is why most at-home hair dyes suggest applying the product on unwashed hair. As the ends are often not exposed to many of these protectant oils, coloring the hair can be a cause of split ends.
On a daily basis, the manner in which hair is handled is one of the primary causes of split ends. Roughly brushing or combing wet hair is one of the main causes of split ends in otherwise healthy hair, as the hair shaft is weakest when wet. In general, wet hair should be treated very delicately. Even roughly brushing through dry, tangled hair can result in excessive damage to the ends, as can pulling out elastic holders, clips, or pins without untangling the hair first.