Technicaly speaking, this
phenomenon is alled 'Trichoptilosis' and is the logitudinal splitting of the hair
fibre. It is the cause of the stripping of the protective
cuticle from the ends of a
hair shaft, often as a result of over-processing. This could be through
chemical trauma, such as
bleaching or repeated dying. It could also be the result of
physical trauma, such as
brushing your hair while it is still wet or letting it get
loose and lash about in windy environments, especially
warm windy environments. It more commonly happens to brittle hair while suffering from other hair shaft defects such as
bamboo hair (trichorrhexis invaginata), monilethrix, trichothiodystrophy, Netherton's syndrome, and pili torti.
Usually the shaft may split two or three ways, and the split may range from some mm to 3 cm. more severe damage however, induces more severe splitting. Splits may run many cm long in very weathered hair.
On some occasions, the hair splitting may occur towards the middle of the hair shaft due to cuticle stripping but are held by one strand at the shaft.
There is no way of replacing the cuticle form the hair once it is removed. There are certain treatments that involve gluing the hair, but these don't last long and don't work too well. the best way to remove split ends is to cut the hair - sometimes drastic cuts need to be made, since the line of damage in the shaft might run longer than one imagines and the splits will reappear in a matter of days. But they will not go on their own and delaying the trimming will only make the situation worse, since the split is likely to lengthen.
Finally in the case of the dreaded Trichoptilosis, prevention is defintely better than cure. So if you are completely vain (like moi), avoid getting your hair wet with salt water and sunbathing, use only a wide toothed comb while combing as-yet-wet hair, do not sit in cars with windows open in hot weather and never ever use rubber bands to tie your hair up - use only soft-material-covered scrunchies.