In women, hair thinning at the crown could be a sign of alopecia. Most commonly, there are two types of alopecia: androgenic (or hormonally-triggered hair loss) and alopecia areata (an autoimmune disease), says Deanne Mraz Robinson, MD, FAAD, the chief medical officer of Ideal Image.

Insufficient Moisture and/ or Protein More often than not weak, brittle natural hair is due to lack of moisture or protein. It may also be a combination of both. You may need to increase how often you deep condition, use protein treatments, and/or remoisturize your hair.