The bad news is that you can’t really “repair” or heal your already damaged hair. Your hair is technically dead. It has no nervous system, blood, or cell regeneration. Once the hair goes beyond the roots it is no longer living tissue and as such it does not have a regenerative ability, thus it cannot heal.
You can use products such as oils and conditioners to temporarily hide and manage damaged hair but they will not repair your strands. The products can, however, improve your hair texture and appearance and offset more damage with protective ingredients.
Hair can dehydrate and quickly become damaged for many reasons such as being over processed, colour treated and burnt. Hair can lose its moisture and eventually grow brittle if it is not conditioned continually, helping stall more damage. But the damage that has already been created, is ultimately irreversible.
Damaged hair has less elasticity, is prone to breakage and splitting. Split ends are absolutely not repairable and are very challenging to conceal, especially when there are a lot, they must be cut off.