Hair fails to maintain moisture levels: When you bleach hair, hair loses its moisture and it then becomes difficult to maintain protein balance in it too. Your hair, thus, becomes prone to damage as well as breakage. Bleaching hair means using strong chemicals on your otherwise sensitive hair.
Not only does bleaching raise the outer cuticle, it also damages bonds inside the hair too (hair is made up of three types of bonds: hydrogen, disulfide and salt bonds) causing them to weaken and break, and when internal structure of hair is compromised, strands are more likely to split and snap.