hi,,,,you could get heat damage from using a heating appliance too high on your hair or using it on wet hair which can cause the cuticle to explode which would cause breakage,, if your have hair that cannot seem to curl up and seems hard and crispy it may be heat damaged,,, if you have excessive split ends you may have some heat damage.... you really cannot repair damaged hair, it needs tobe cut sooner or later BUT you can use protein treatments such as Kpak , aphogee , paul mitchell hair repair treatment etc once a week unless your hair feels hard....when you use a heat appliance make sure youre using a heat protectant , spray or serum .... and do not iron on the hottest setting, dont keep the iron in one place too long,, dont do too many strokes on one piece of hair..hope that helps