Stress: Up to 6 months after a stressful time, a person can lose her hair
Low thyroid: Very common cause for thinning of the hair, often severely
Nutrient deficits: Biotin, zinc, essential fatty acids
Toxic exposures: Mercury, arsenic (yes, believe it or not)
Parasitic and allergic reactions
Hormone imbalance for women between estrogen, progesterone, and testosterone