Some research has been done that shows that there are some cases of hair loss in postmenopausal females that are caused by genetic factors, but most are caused by hormonal changes. Women who have certain genes that make it more likely for the thyroid gland to produce too much progesterone are more susceptible to hair thinning than women without these genes. Hormone levels may also play a role in the loss of hair. Many women who have undergone surgery may have reported thinning hair after their surgery.