Updated: Mar 30
Hair thinning is actually a very common issue that I see in the clinic, and it can be extremely distressing. In this article, I will review some of the causes of hair thinning that I test for, and some solutions to get your hair growing again. One important thing to note is that getting the hair into a re-growth cycle can be frustratingly slow, even once you have begun to treat the underlying cause. This is why I strongly recommend lab testing so that we can be confident (and patient) with your treatment plan, as it can take several months to see progress here. The good news is that with proper assessment, you can get to the root of your hair loss issues, and in almost all cases the hair will grow back normally.
Causes of female hair loss:
I have identified 10 of the most common causes of female hair loss below. In each section, you can learn how to identify or assess with lab testing, and appropriate treatment.
1. Iron deficiency
Iron deficiency is by far the most common cause of hair thinning, and it often shows up very gradually, and is diffuse meaning all over the head. This is the most likely cause if you have heavy periods, are vegetarian or rarely eat red meat. There are some less common causes of iron deficiency related to nutrient absorption in the gut which would be assessed if iron intake is excellent and periods are light.
Testing is very simple with bloodwork to look at your hemoglobin and iron stores (ferritin). As a general rule, ferritin levels need to reach 40 ng/mL for hair regrowth to begin.
Treatment for iron deficiency includes: iron supplements to bring up iron stores, and strategy to deal with the causes (iron intake, heavy periods, iron absorption).
2. Metabolic stress
With recent diet trends and intense exercise programs, metabolic stress is also a very common cause of female hair loss. Metabolic stress is a term for insufficient nutrient or caloric intake relative to energy output. It can be triggered by low calorie intake, low carbohydrate intake, low fat intake, fasting, and over-exercising. Most women who I see with hair thinning due to metabolic stress have got here by accident through following recent health trends like a ketogenic diet, intermittent fasting or too many high-intensity workouts.
It is important to recognize that women’s bodies are VERY sensitive to metabolic stress, and make hormone compensation in response to these stresses. Women also respond completely differently to men with these practices, and especially during peak ‘reproductive’ years (20’s and 30’s).
There is a blood test that can point to metabolic stress, and this is for free T3, one of your thyroid hormones. When free T3 drops, your body is literally slowing down your metabolism in response to low calorie intake or high energy output. Hair thinning is usually the first symptom, followed by fatigue with irritability, dry skin, depression, constipation, poor injury recovery, possibly loss of periods and more. If you want to learn more, I have written about metabolic stress several times relative to intermittent fasting, ketogenic diet and also overtraining syndrome.
Treatment for hair loss due to metabolic stress is to quite simply ensure that your body is properly nourished, that you are eating enough for your exercise output, and carefully examine whether nutrition trends are working for your body. It can take several months for free T3 levels to reset after a period of metabolic stress, after which the hair will begin to grow back.
3. Androgen excess
The most common cause of androgen excess is PCOS (polycystic ovarian syndrome), and in some cases hair thinning an also accompany acne, extra hair growth (body and face), and irregular menstruation. There are other hormone imbalances that can cause androgen excess too: NCAH (non-classic congenital adrenal hyperplasia), high testosterone levels, or issues with androgen clearance causing high DHT (dihydrotesosterone) levels.
If there are signs of androgen excess present, such as: cystic acne, oily skin, or coarse hair growth on the face, lab testing to check androgen levels is highly recommended.
Treatment for androgen excess depends on the underlying cause. With PCOS we often address insulin resistance, and in other cases we support the body to detox and clear androgens with herbs such as saw palmetto, and minerals like magnesium and zinc.
4. Under-active thyroid
Low thyroid function can cause hair thinning among other signs, which include weight gain (or difficulty losing weight), feeling cold and lower body temperature, constipation, dry skin, longer menstrual cycle, difficult fertility, brain fog, and getting sick more frequently. If any of these other signs are present, thyroid testing is actually quite simple with bloodwork. Just ensure that you are tested thoroughly with a test for TSH, along with free T4, free T3 and thyroid antibody levels. Low thyroid is most commonly diagnosed at times of hormone transition, such as pregnancy, postpartum and menopause.
5. Hormonal contraceptives
Some hormonal contraceptives trigger hair loss, as can changing birth control pills or stopping the pill. A sudden shift in your hormones may be the cause. The good news is that these changes are usually reversible, and the hair will grow back again within a few months of adapting to a new hormonal norm. One note here is that some women experience signs of “temporary PCOS” coming off hormonal birth control with irregular or missing periods, acne and hair thinning. Proper assessment with lab testing is recommended, not only a pelvic ultrasound to confirm.
If you suspect that a change in hormonal contraceptives is causing your hair thinning, make sure you also check for other possible causes too: low iron, thyroid, stress hormones and insulin resistance. It is quite common that there may be two underlying issues.
Most women are aware that a period of very high stress can cause temporary hair thinning. Both a rise in cortisol levels, or DHEA levels (our ‘overdrive’ adrenal hormone) can trigger hair thinning. Both of these hormones can be tested with basic bloodwork, salivary hormone panels, or dried urine testing (DUTCH test).
Stress can also cause a different form of hair loss called alopecia areata where a small usually round bald patch appears on the scalp. If it is just one or at most 2 small patches, and you are currently going through a high stress period, use this as a sign to adopt some restorative self-care practices. If there are more patches of hair loss or it is spreading, please read below for autoimmune causes.
7. Postpartum hair loss
Those of you who have had babies are familiar with this one! So much of the lovely thick hair that you grew during pregnancy is shed somewhere between 3-6 months postpartum, and it can be alarming! Although this is a normal biological process, if the hair thinning seems excessive especially around the hairline and temples, I would highly encourage some lab testing to ensure that your iron levels are sufficient (ferritin should be above 40ng/mL) and that your thyroid function is optimal (TSH should be between 0.8-2.5mU/L). Iron deficiency from blood loss during childbirth, and post-partum thyroid issues are quite common and also easily treatable.
Postpartum hair loss does fill in, usually within the first 18 months after childbirth, and should leave you with hair just as thick as pre-pregnancy.
8. Insulin resistance
One less-known symptom of insulin resistances is hair thinning, and in fact this is extremely common in women as they age if their blood sugar and insulin levels are not optimal. Insulin resistance occurs when you are over-eating high carbohydrate foods and sugars, and your body over time starts to produce too much insulin in response. Other signs of insulin resistance include: weight gain around the central abdomen, fatigue and fogginess after eating, strong cravings for sweets and carbs, and sometimes sleep disruption. If left untreated, insulin resistance can lead to diabetes.
Insulin resistance usually causes diffuse hair thinning on the crown of the head that gradually progresses over time.
Testing for insulin resistance can be done with morning, fasting bloodwork looking at glucose and insulin levels. Treatment for insulin resistance is largely focused on a long-term nutrition plan with less carbohydrates and simple sugars, more physical activity, stress reduction and optimizing sleep. You can learn more about insulin resistance here.
9. Chemical treatments and hair extensions
Chemical treatments ranging from dyes, straighteners and perms can all cause damage to the hair and the scalp leading to hair thinning, and sometimes temporary hair loss.
Hair extensions can also cause stress on the hair, pulling out and gradually thinning the hair where they are attached.
If you’re noticing these possible causes of hair issues, please discuss safer options with your hair stylist that will cause less stress on your hair and scalp.
Although this is not a common cause of hair thinning, it is important to mention to ensure that you are assessed properly if you have significant hair thinning. Autoimmune alopecia is the most dramatic type of hair loss, which can occur in patches or through the whole scalp. Two things that make this type of hair loss different from the ones above are: 1) hair loss usually includes eyebrows, eyelashes and body hair; and 2) the patches of hair loss are completely bald, not thinned.
As with many other autoimmune conditions, a naturopathic or functional medicine approach can be taken to check for immune system triggers (food sensitivities, gluten intolerance or celiac disease, gut microbiome imabalances or toxins which can trigger autoimmunity. If treated early on, I have seen some cases of autoimmune hair loss reverse by treating the underlying cause of the autoimmunity, not just the scalp.
Lab testing for female hair loss
As mentioned above, it is very important to do lab testing to understand possible causes of hair loss. We can gain some clues based on the location of hair thinning, and also clinical clues with timing so in most cases we do not need to run all of these tests. Here are some to consider:
Nutrient deficiencies: Iron (ferritin, serum iron, Hb), zinc
Thyroid function: TSH, fT4, fT3
Stress hormones: Cortisol, DHEA
Blood sugar and insulin: fasting glucose and insulin
Androgen levels: free & total testosterone, DHEA, androstenedione, DHT (dihydrotestosterone)
Inflammatory markers: CRP, ESR, ANA.
As mentioned at the start of the article, changes in hair re-growth can take time and patience. This is why it is extremely important to assess properly first so you can maintain confidence in your treatment plan.
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