What are the underlying medical conditions that can cause hair loss?

The top 6 medical conditions that can cause hair loss are:

1) Cancer – treated with a chemotherapy agent based on the location of a tumour.
2) Obstetric and gynaecological conditions that can cause post-partum and post-menopausal states.
3) Anaemia – deficiency of iron.
4) Thyroid disease.
5) Connective tissue diseases, such as Lupus.
6) Poor nutrition, such as the result of crash diets, often resulting in a deficiency of protein, calcium, essential fatty acid and zinc.