What could cause my hair to fall out?

Many: Thryoid disease, tinea, stress, age.

Few common ones: Severe and prolonged illness, chemo, medication/withdrawal of such (i.E ocps), and following pregnancy are few common examples of causes of hair loss(falling-out). These will grow back in time. U lose about 150 hair per day, but those with longer hair and braid/tie their hair see fall-out more during showering because the fallen hair are still held in tie until release/shower/brushing. Good luck.