There are 100,000 to 350,000 hair follicles on the human scalp that go through cyclic phases of growth and rest. Hair growth slows by age 40, and several hormonal factors can influence the duration of hair cycles. Sex hormones can affect hair growth in women through two pathways: estrogen dominance and rarely testosterone metabolism.
The most common sex hormone related factor causing an overall hair thinning, loss or lack of regrowth is estrogen dominance. Estrogen dominance is a term defined by Dr. John Lee and refers to the relative deficiency of progesterone levels in relation to estrogen levels that often develop in our late 30s or 40s. Other symptoms of estrogen dominance include irregular periods, heavy periods, water retention, breast tenderness, mood swings, insomnia and depressed mood or anxiety. This can be confirmed by checking hormone levels during the luteal phase of a woman’s cycle and can be treated with cyclic progesterone supplementation.
Testosterone replacement in a very small percentage of women can cause androgenic female pattern hair loss. This resembles the receding hairline and thinning crown seen in male pattern baldness. These women seem to metabolize an unusually large percentage of their testosterone down a specific pathway, resulting in an increase in the metabolite DHT (dihydrotestosterone). Some women benefit from adding saw palmetto to their regimen to prevent this shift, while others simply discontinue all testosterone replacement.
The most important hormone involved with hair is thyroid. Hypothyroidism symptoms include dry, brittle hair or hair loss or hair thinning. Thyroid issues can be assessed and ruled out through blood testing. Prevalence of hypothyroidism in American women is 12 percent, and many are undiagnosed. Other symptoms of hypothyroidism include constipation, cold extremities, weight gain and fatigue. If a patient is diagnosed with hypothyroidism, the treatment is an oral medication containing thyroid hormones.
If both thyroid and sex hormone factors have been treated or ruled out, there are still options. Several prescription and over-the-counter medications – such as NSAIDS, antibiotics, antidepressants, anti-epileptics, gout mediations, ulcer medications and chemotherapy medications – can cause hair loss. Some of these medications, such as ulcer medications, cause nutritional deficiencies – including zinc, vitamin A, essential fatty acids and iron – that in turn cause hair loss.