There are many reasons why hair loss occurs in females. Besides thyroid problems, hair loss can be due to menopause and associated hormone changes. Hair loss can also occur if you've recently lost a lot of weight or undergone a trauma or extreme stress. Sometimes it's hereditary---did your mother, grandmother and/or aunts experience this around your age? Some skin conditions are also linked with hair loss. And overprocessing your hair (dyes, straighteners, etc.) can also damage the hair and lead to hair loss.

Since you seem to have eliminated the thyroid as a source of your problem, you should consider seeing a dermatologist to help you figure out what is causing your hair loss and the best way to treat it. Good luck!

When you had the thyroid function test performed were all three levels checked which would be TSH (thyroid stimulating hormone), T3 and T4 thyroid hormone levels? Most commonly it is the TSH test that is performed exclusively, which can be inaccurate. In addition, labs typically use a range of .5 - 5.0 as being the norm for TSH levels. Endocrinologists are now recommending that the ideal range be 0.3 -3.0. T3 and T4 are the actual thyroid hormone levels, (not thyroid stimulating hormone level).

I do have hypothyroidism and it was not detected for several years from the time the symptoms commenced. The TSH result was initially normal therefore hypothyroidism was dismissed. Within a short period of time my hair began noticeably thinning, other symptoms included fatigue, tendency to gain weight, cold intolerance, brittle hair and nails, moodiness, etc.. When it was rechecked, the TSH levels were way over the norm, (which indicates hypothyroidism). Hyperthyroidism can cause hair loss as well. If there is any question, consider having a re-test, (TSH, T3 and T4) using the endocrinologist suggested levels to determine the normal range.

Women do begin experiencing changing hormone levels at 40, including reduced estrogen levels which can result in an estrogen-androgen imbalance which can contribute to hair loss. Thyroid dysfunction commonly occurs during this time as well. Synthetic estrogen replacement, (such as Premarin), can cause substantial hair loss and interfere with thyroid medication/function.

Other causes of female hair loss can include anemia/iron deficiency, medications, stress/illness, malnutrition, high fever, trauma, shock, autoimmune disorders (such as diabetes, lupus, Addison's disease and rheumatoid arthritis) and scalp conditions such as psoriasis and seborrhea.

Discontinuing birth control pills or hormone replacement can result in sudden hair loss, as can taking retinoids, some blood pressure medications, anti-depressants, and even NSAIDS (such as ibuprofen).

Personally, I would suggest that you have the thyroid and hormone levels rechecked because of the hair loss and the fact that you are near 40. Excessive hair loss is not normal and can be reversed if the cause is identified. I wish you well.

All of these are good answers. My contribution is 'stress' and stress-related hair loss. Being under stress can cause a woman (or a man) to lose their hair. You might want to discuss you hair loss with your medical provider.