You keep finding more hair on your pillow, in the shower or in your brush. Perhaps your ponytail is thinning or you can see more scalp through your hair. Hair loss in women is surprisingly common, and it often affects you more than expected. But it is not just a cosmetic issue. Hair loss can be a signal that something in your body is out of balance.
In this article, we explore the most common hormonal and nutritional causes of hair loss in women, which blood values to test and how your results can guide targeted action.
Hair loss is more than aesthetics
Hair is one of the fastest-dividing tissues in your body, making it extremely sensitive to changes in hormonal balance, nutritional status and overall health. When something is off with your iron stores, thyroid function or hormone levels, your hair is often one of the first places you notice. In other words, hair loss is your body talking to you.
When is hair loss abnormal?
Everyone loses around 50 to 100 hairs daily as part of the natural growth cycle. But if you are consistently losing more, notice patches or find your hair getting thinner, there may be an underlying cause. In women, hormonal shifts and nutritional deficiencies are the most common culprits. Hair loss often appears with a delay of two to four months after the trigger, which makes a blood test especially valuable for identifying the root cause.
Ferritin: the most underestimated cause
Ferritin reflects your iron stores. Low ferritin is one of the most common causes of hair loss in women, yet it is frequently overlooked. Your haemoglobin may still be normal while ferritin has already dropped significantly. Hair is one of the first areas where your body cuts back when iron stores are depleted.
Many doctors consider a ferritin above 15 µg/L as normal, but healthy hair growth typically requires levels of at least 40-70 µg/L. Some dermatologists recommend levels above 80 µg/L for optimal hair growth. If you menstruate, eat a vegetarian diet or exercise intensively, checking your ferritin is particularly worthwhile.
For a complete picture of your iron status, also consider testing iron and transferrin saturation.
Thyroid hormones: the silent disruptor
Your thyroid regulates metabolism and directly influences the hair growth cycle. Both hypothyroidism and hyperthyroidism can cause hair loss. Thyroid conditions occur five to eight times more frequently in women than in men.
With an underactive thyroid, hair becomes dry, brittle and thin, often with diffuse thinning. You may also notice thinning eyebrows, particularly the outer third. The most important marker to measure is TSH. If TSH is abnormal, measuring free T4 as well provides a more complete picture. Even subclinical thyroid dysfunction, where TSH is slightly off but free T4 is still normal, can cause symptoms including hair loss.
Oestrogen and progesterone: hormonal shifts
During periods of major hormonal change, such as menopause, after stopping the pill or after pregnancy, hair loss can occur. Oestrogen has a protective effect on hair growth, so when oestradiol drops, the growth phase of hair shortens and more hairs enter the shedding phase simultaneously.
A decline in oestradiol combined with low progesterone can contribute to diffuse hair loss. Postpartum hair loss is almost universal: high oestrogen during pregnancy keeps hair in the growth phase, and the abrupt drop after delivery triggers a mass shedding two to four months later. This is nearly always temporary.
Testosterone and DHEA-S: androgenetic alopecia
Androgenetic alopecia is not just a male condition. In women, it manifests as thinning around the crown and a widening parting, while the hairline usually remains intact. An estimated 40% of women experience it to some degree, especially after menopause.
The two relevant markers are testosterone and DHEA-S. However, androgenetic alopecia can occur even with normal androgen levels, as the hair follicle itself may be hypersensitive to DHT (dihydrotestosterone). If PCOS is suspected, also check the FSH-to-LH ratio.
Zinc: the forgotten mineral
Zinc plays an essential role in cell division, protein synthesis and keratin production, all crucial for hair growth. Deficiency is more common than you might think, particularly in women on vegetarian diets, hormonal contraception or experiencing chronic stress.
When to take action
Consider getting a blood test if you consistently lose more than 100 hairs per day for over six weeks, notice patchy bald spots, your hair becomes visibly thinner at the parting or crown, hair loss coincides with fatigue, weight changes or cycle irregularities, or if hair loss began after stopping the pill, pregnancy or around menopause. The sooner you identify the cause, the more effective the approach. Hair loss from nutritional deficiencies is often fully reversible when addressed in time.
Which test is right for you?
For fatigue with thinning hair, start with an iron panel including ferritin. For suspected hormonal causes, choose a comprehensive hormone test covering oestradiol, progesterone, testosterone and DHEA-S. For thyroid-related symptoms, test TSH and free T4 specifically. Often a combination test is the most informative.
Frequently asked questions
Can stress cause hair loss?
Yes. Severe or prolonged stress can lead to telogen effluvium, a form of diffuse hair loss that begins two to four months after a stressful period. It pushes a large percentage of hairs from the growth phase into the shedding phase simultaneously. This type of hair loss is nearly always temporary and typically recovers within six to twelve months once the stress factor resolves.
How quickly will you see results after treatment?
For iron deficiency, improvement may be visible after three to six months of supplementation. For thyroid issues, medication can take several months to affect your hair. Hair grows approximately 1 cm per month, so patience is essential. The first improvement you notice is usually less hair falling out, followed later by new growth.
Which test is most informative for hair loss?
No single test covers everything. The most valuable combination is ferritin, TSH, oestradiol, testosterone and zinc. These values help rule out the most common hormonal and nutritional causes. Depending on the results, further investigation may be needed.
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