Why Hair Breaking Off?

Hair breakage can be a serious problem whether or not you're trying to attain length. If your hair is breaking off faster than it's growing, it may seem like your hair isn't growing at all. Unless you have a medical condition, your hair is growing, but retaining length is important for seeing this growth.
Look at where the breakage is occurring. Is it at the ends of your hair? Or is the breakage at the crown of your head? Depending where the breakage is can help you determine the reason.

the answer is : 
Dry ends: If you notice a lot of breakage on the ends of your hair, they could be excessively dry. This can be due to too much heat styling. If you flat ironor hot curl your hair too frequently, this can explain why your ends "pop" every time you comb them.
Another reason your ends may be extremely dry is lack of conditioning. Do you condition your hair after every shampoo? Do you deep condition on a regular basis as well as use a leave-in conditioner? Black hair needs moisture to thrive.

Also, are you using a comb with widely spaced teeth? If your comb has teeth that are too close together, they may be pulling on your tangled ends and causing breakage.
Solutions for dry, breaking ends include regular deep conditioning, daily conditioning with moisturizing treatments, using a comb with teeth wide enough to work through your hair (particularly natural hair) and easing up on heat styling.

Styling issues: Maybe you notice breakage in the crown area. This may have more to do with styling techniques. Are you wearing tight ponytails or are you using elastics with metal pieces? The wrong type of hair accessories can "catch" and break your hair off. Styles that are too tight can also cause breakage.

To solve this, try using ponytail holders with no metal parts or covered elastics. You should also try different styles, especially ones that don't pull too tightly on your hair.

Overlapping chemical processes: If your hair is relaxed and you touch-up more than the new growth, overlapping the relaxer onto previously relaxed hair can cause breakage. Touch-ups are a tricky area for many people.

Hair color can also cause breakage, if used too often or on top of other chemical processes that leave your hair dry. Hair colors that involve bleaching before depositing new color onto the hair can be especially harsh on hair that's already relaxed or texturized.

If possible, you should see a professional for relaxer touch-ups, even if you can easily maintain your hair on a daily basis. While hair rinses are generally safe enough for anyone to use at home, complicated color processes should also be done by stylists.