Split ends happen when hair has been damaged. The hair shaft actually splits into two or more pieces. This usually happens at the end of a strand of hair. If you have some breakage higher than the end of the strand, it can also become a split end. The tiny hairs and fly-aways that seem to stick straight out of your head are sometimes split ends, too. Other times they're simply broken hairs. Once the protective layer around your hair has broken, then a split can occur. The split can travel all the way up the hair shaft. Cutting hair above the split is the only way to stop it from traveling further.
The cause of split ends is damage to your hair. The biggest causes of damage are over-brushing, heat styling and chemical treatments like relaxing or dying. For many people, some of these damage-causing practices are unavoidable or necessary. There are still ways to prevent damage, even if you don't want to throw away your curling iron. Other causes of hair damage include chlorine from swimming or tap water, salt water, sun, hair accessories like bands with metal clips or barrettes with clasps that snag, extensions, braiding, brushes with sharp bristles, fine combs and coming or brushing hair while wet.
Treating your hair a bit more gently will go a long way in preventing split ends. You will probably not be able to get rid of them completely, but combining good hair habits with regular trims every 4 to 6 weeks will keep your hair in its best health possible. Avoid over-processing your hair. If you dye and relax your hair, choose only one chemical treatment. Instead of dying your hair multiple times, just touch up roots when needed. Do not strip your hair every time you color it. Instead of bleaching hair, try a dye that contains bleach for a little less damage. Always rinse your hair after swimming. If you have high chlorine content in your water at home, consider buying a filtered shower head. Only brush or comb hair when it's dry. Do not over-brush it. Choose the right conditioner for your hair. Most manufacturer websites have quizzes to help you find the right product. Buy only hair ties that are ouch-less or that have no metal clip on them. Do not use heat styling tools if you don't need to. If you do use them, be sure to apply a heat protecting spray to your hair first and comb it through.