Hair Loss in Women and Men: Hormones, Thyroid, Iron, Testosterone and What to Test
Hair loss is common, but that doesn't mean it should automatically be dismissed as genetics, stress or "just getting older."
Whether you're a woman noticing a widening part during perimenopause, a man experiencing thinning at the temples or crown, or someone suddenly finding significantly more hair in the shower, hair loss can have multiple contributing factors.
Hormonal changes, thyroid function, iron status, nutritional deficiencies, genetics, medications, metabolic health, illness, stress and significant weight loss can all influence the hair-growth cycle.
That's why when someone tells me, "I'm losing my hair," my first thought isn't which supplement they should buy.
It's: Why is this person losing their hair?
Before spending hundreds of dollars on supplements marketed for hair growth, it may make more sense to identify whether there is actually something that needs to be corrected.
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Before Buying Another Hair Supplement, Consider Testing
Hair-loss supplements are everywhere. Biotin. Iron. Zinc. Vitamin D. Collagen. B vitamins. Multinutrient hair formulas.
But the problem with starting supplements first is that you may be treating something you don't actually have while missing the factor that is contributing to your hair loss.
For example, iron supplementation makes sense when iron deficiency is present. But more iron isn't automatically better. The same applies to zinc, vitamin D, B12 and other nutrients. And hair loss may have nothing to do with a nutritional deficiency at all.
It could be related to:
Thyroid dysfunction
Hormonal changes
Perimenopause or menopause
Androgen-related hair loss
Significant weight loss
Recent illness or surgery
Medications
Stress
Genetics
An autoimmune or dermatologic condition
Testing isn't about ordering every laboratory test available. It's about determining which tests make sense based on the individual.
The laboratory tests discussed in my social media content are examples of testing I may consider based on a person's symptoms, medical history and clinical picture. Not every person experiencing hair loss needs every test listed.
Hair Loss Is a Symptom, Not a Diagnosis
There are many different types of hair loss. Two of the most common are androgenetic alopecia and telogen effluvium.
Androgenetic alopecia
Androgenetic alopecia is commonly known as female pattern hair loss in women and male pattern hair loss in men. It is the most common hair-loss disorder in both men and women and involves progressive miniaturization of genetically susceptible hair follicles.
In men, this commonly appears as recession around the temples or thinning over the crown. Women more commonly notice diffuse thinning over the top of the scalp, reduced hair density or a widening part.
Telogen effluvium
Telogen effluvium typically causes more generalized shedding. It can occur after a physiologic stressor such as:
Significant illness or fever
Surgery
Major emotional or physical stress
Childbirth
Rapid or significant weight loss
Inadequate calorie or protein intake
Nutritional deficiency
Thyroid dysfunction
Certain medications or medication changes
One of the most important things to understand about telogen effluvium is that shedding may not begin immediately. It can become noticeable approximately two to three months after a triggering event, which means the cause may be easy to overlook.
Hair Loss During Perimenopause and Menopause
Hair changes are especially common during midlife, perimenopause and menopause. Women may begin noticing:
A widening part
A thinner ponytail
Increased shedding
Thinning around the crown
More visible scalp
Changes in hair texture
Slower hair growth
Hair follicles respond to hormonal signaling, and the hormonal environment changes considerably during the menopause transition. Estrogen and progesterone fluctuate and eventually decline, while the relationship between estrogen and androgen activity changes as well.
That doesn't mean every woman experiencing hair loss during perimenopause has an estrogen deficiency that needs to be treated. A woman in her 40s or 50s may have several things occurring simultaneously:
Hormonal changes
Heavy or irregular menstrual bleeding affecting iron stores
Thyroid dysfunction
Changes in nutrition
Significant stress
Weight loss
Female pattern hair loss
Medication changes
This is one of the reasons midlife hair loss is often multifactorial.
Can Low Estrogen Cause Hair Loss?
Estrogen appears to influence normal hair-follicle biology, and changes in estrogen during menopause may contribute to changes in hair growth and density. However, hair loss during menopause should not automatically be attributed to estrogen deficiency. Research into estrogen therapy specifically for menopausal hair loss is still evolving.
Hormone therapy should therefore be considered based on a woman's overall symptoms, health history, potential benefits and risks, and appropriate indications rather than prescribed solely because she is losing hair.
Hair Loss in Men: Testosterone, DHT and Genetics
Hair loss isn't just a women's hormone issue. Male pattern hair loss, or androgenetic alopecia, is extremely common in men. Genetics and androgen signaling both play important roles.
Testosterone can be converted by the enzyme 5-alpha-reductase into dihydrotestosterone, or DHT. In genetically susceptible scalp follicles, DHT contributes to progressive follicular miniaturization. Over time, hairs become shorter, finer and less visible.
But this leads to an important misconception.
Does Male Pattern Hair Loss Mean Testosterone Is High?
No. Male pattern hair loss does not automatically mean a man has high testosterone. Two men can have similar circulating testosterone levels and completely different patterns of scalp hair. Genetics, androgen-receptor activity and the sensitivity of individual hair follicles to DHT matter.
Can Low Testosterone Cause Hair Loss?
Men sometimes assume that thinning hair means they have low testosterone. Classic male pattern scalp hair loss is not simply a symptom of low testosterone.
However, if a man is experiencing hair changes along with symptoms that raise concern for testosterone deficiency, a broader hormone evaluation may be appropriate. Symptoms associated with possible testosterone deficiency can include:
Reduced libido
Erectile changes
Fewer spontaneous or morning erections
Reduced muscle mass or strength
Increased body fat
Reduced body or facial hair
Changes in energy
Other symptoms consistent with androgen deficiency
Hair loss alone should not be used to diagnose low testosterone. When testosterone deficiency is suspected, the diagnosis should be based on the clinical picture together with appropriately obtained laboratory testing. Depending on the individual, testing may include:
Total testosterone
Free or calculated free testosterone
SHBG
LH
FSH
Prolactin when indicated
Additional testing based on the history and initial results
Can Testosterone Replacement Therapy Cause Hair Loss?
Another common question is whether testosterone replacement therapy, or TRT, causes hair loss. Not necessarily. However, because testosterone can be converted into DHT, increasing androgen exposure may potentially accelerate androgen-related hair loss in someone who is already genetically susceptible to male pattern hair loss.
That is very different from saying that testosterone therapy automatically causes baldness. Genetics and follicular sensitivity remain important. It is also one reason testosterone therapy should be appropriately evaluated and monitored rather than managed simply by trying to reach a particular testosterone number.
Androgens and Hair Loss in Women
Women produce testosterone and other androgens too. Androgen signaling may contribute to certain forms of female hair loss, but female pattern hair loss can occur even when circulating androgen levels are not elevated.
Hormonal testing may become particularly relevant when thinning hair occurs along with symptoms such as:
Increased facial or body hair
New or worsening acne
Irregular menstrual cycles
Signs suggestive of PCOS
Rapidly progressing hair loss
Other symptoms of androgen excess
Depending on the clinical picture, testing may include testosterone, free testosterone, SHBG, DHEA-S or other endocrine testing. Again, the goal isn't to test every hormone in every woman. Testing should answer a clinical question.
Iron, Ferritin and Hair Loss
Iron status is an important consideration when evaluating diffuse hair shedding. It can be particularly relevant for women experiencing:
Heavy menstrual bleeding
Frequent or prolonged periods
Frequent blood donation
Restrictive diets
Gastrointestinal conditions that affect nutrient absorption
Significant dietary changes
Ferritin gives us information about stored iron, while iron studies provide additional information about iron availability and transport. A person can develop depleted iron stores before developing overt anemia, which means looking only at hemoglobin may not provide the entire picture.
However, there is not one universally accepted "optimal ferritin" number that guarantees hair growth. This is why I prefer testing and clinical context rather than automatically recommending iron. More iron isn't automatically better.
Thyroid Problems and Hair Loss
Thyroid function and hair growth are closely connected. Thyroid dysfunction can disrupt the normal hair-growth cycle and contribute to diffuse shedding.
A thyroid evaluation frequently begins with TSH, often along with free T4 depending on the situation. Additional testing may sometimes be appropriate based on symptoms, medical history, known thyroid disease, autoimmune history, previous laboratory abnormalities, medications, or initial thyroid results ā which might include additional thyroid testing or thyroid antibodies when clinically indicated.
This does not mean that every person with hair loss automatically needs a comprehensive thyroid panel. The testing should fit the patient.
Nutritional Deficiencies and Hair Loss
Hair follicles are metabolically active and depend on adequate nutrition. Depending on someone's medical history, dietary pattern, medications and symptoms, nutritional evaluation may include consideration of:
Ferritin and iron
Vitamin B12
Folate
Vitamin D
Zinc
Copper when indicated
Protein intake
Overall caloric intake
Methylmalonic acid may sometimes provide additional information when evaluating vitamin B12 status.
Don't Spend Hundreds on Supplements Before Testing
A product marketed for hair growth may contain multiple vitamins and minerals. That doesn't mean you're deficient in them. Taking something simply because it is marketed for hair loss can make it difficult to determine what was actually deficient, may expose you to nutrients you don't need, and still doesn't address hormonal, thyroid, metabolic, genetic or dermatologic causes.
The goal isn't more supplements. The goal is identifying what actually applies to you.
Rapid Weight Loss and Hair Shedding
Significant or rapid weight loss is another possible trigger for hair shedding. When the body undergoes a major physiologic change, a greater percentage of follicles may transition into the resting phase of the hair-growth cycle. Potential contributors can include:
Rapid weight loss
Significant calorie restriction
Reduced protein intake
Changes in nutrient intake
The physiologic stress of major weight change
Because telogen effluvium is delayed, shedding may become noticeable months after the weight loss began.
Medical Weight Loss and GLP-1 Medications
Hair loss has also become a frequent question among people using GLP-1ābased medications for medical weight management. Recent research has reported hair loss among people using these medications, although researchers are still working to better understand the relationship. There may be several overlapping factors:
The medication itself
Speed or magnitude of weight loss
Reduced calorie intake
Reduced protein intake
Changes in micronutrient intake
Preexisting hormonal or thyroid issues
An underlying predisposition to hair loss
If hair shedding develops during medical weight management, the entire clinical picture deserves consideration. It does not automatically mean someone should stop a medically appropriate medication.
Does Metabolic Health Affect Hair?
Metabolic health can also be relevant in certain patients. Insulin resistance and metabolic dysfunction can interact with inflammatory and hormonal pathways, and researchers have examined associations between metabolic abnormalities and androgenetic alopecia. Depending on someone's overall health history and risk factors, metabolic testing may include:
Fasting glucose
Hemoglobin A1c
Fasting insulin in selected individuals
Additional cardiometabolic testing when appropriate
These aren't mandatory "hair-loss labs." They are considered when the person's overall clinical picture suggests metabolic dysfunction may also deserve attention.
Stress, Illness and Surgery Can Show Up in Your Hair Months Later
When someone tells me, "My hair suddenly started falling out," I want to know what was happening several months earlier. Was there:
COVID or another significant illness?
A high fever?
Surgery?
Major emotional stress?
Rapid weight loss?
Significant calorie restriction?
Pregnancy or childbirth?
A medication change?
A major hormonal transition?
Because the hair cycle responds slowly, the event that triggered shedding may have occurred well before the person noticed a change.
What Labs Should Be Checked for Hair Loss?
There is no universal laboratory panel for hair loss. A thoughtful evaluation begins with the pattern of hair loss, when the shedding started, medical history, current medications and supplements, diet, weight changes, recent illness or surgery, family history, menstrual history when applicable, perimenopause or menopause symptoms, symptoms of possible testosterone deficiency in men, previous laboratory results, and physical examination. From there, laboratory testing can be individualized.
Iron and nutritional evaluation: Depending on the clinical picture, testing may include CBC, ferritin and iron studies. Additional testing such as vitamin B12, methylmalonic acid, folate, vitamin D, zinc or copper may be considered when appropriate.
Thyroid evaluation: TSH is typically the starting point, with additional thyroid testing guided by symptoms, history and initial results.
Hormonal evaluation in women: When indicated, evaluation may include estradiol, progesterone, testosterone, free testosterone, SHBG, DHEA-S, FSH and LH, and prolactin. Menstrual-cycle timing, perimenopause, menopause, hormone therapy and hormonal contraception can all affect interpretation.
Hormonal evaluation in men: Men with symptoms suggesting testosterone deficiency may require appropriately timed testosterone testing, followed by additional endocrine testing when indicated. Hair loss alone does not diagnose low testosterone.
Metabolic evaluation: When metabolic dysfunction is a concern, fasting glucose, hemoglobin A1c and sometimes fasting insulin may be considered.
The purpose isn't to order the biggest panel possible. It's to order the right tests for the right person.
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When Should Hair Loss Be Evaluated by a Dermatologist?
Laboratory testing is only one part of evaluating hair loss. Dermatologic evaluation is particularly important if hair loss is:
Patchy
Rapidly progressive
Associated with scalp redness
Associated with significant scaling
Painful or burning
Significantly itchy
Associated with scarring
Causing eyebrow or eyelash loss
Suggestive of alopecia areata or another inflammatory or autoimmune hair disorder
Some forms of scarring alopecia can permanently damage hair follicles, which makes appropriate recognition especially important.
Hair Loss Is Often Multifactorial
There often isn't one single explanation. A woman in perimenopause could simultaneously have hormonal changes, heavier menstrual bleeding with declining iron stores, significant stress and inadequate protein intake. A man might have genetically driven male pattern hair loss while also experiencing thyroid dysfunction or symptoms that warrant evaluation for low testosterone. Someone else may develop telogen effluvium several months after illness, surgery or significant weight loss. And a patient undergoing medical weight loss may be losing weight quickly while eating substantially less protein.
These people don't all need the same treatment. That's why treating unexplained hair loss by automatically buying another supplement can miss the bigger picture. The first step is determining what may actually be contributing to the hair loss.
Hair Loss, Hormone and Metabolic Evaluation in Seal Beach, California
If you're experiencing unexplained hair thinning or shedding along with symptoms of perimenopause, menopause, hormone changes, thyroid dysfunction, low testosterone, metabolic concerns or significant weight changes, an individualized medical evaluation may help determine whether there are underlying factors that deserve attention.
Core Function Health is based in Seal Beach, California, providing personalized hormone, metabolic and healthy-aging care for adult women and men. I work with patients in Seal Beach and surrounding Orange County and Long Beach communities, including Los Alamitos, Rossmoor, Huntington Beach and throughout California.
For someone experiencing hair loss, evaluation may include a detailed review of hair-loss pattern and timeline, hormonal symptoms, menstrual and menopause history, symptoms associated with low testosterone in men, thyroid history, medications and supplements, nutrition, weight changes, metabolic health, and previous laboratory results. From there, laboratory testing can be individualized rather than assuming everyone needs the same panel.
If you've been searching for answers about hair loss in Seal Beach, hair loss during perimenopause or menopause, hormone-related hair thinning, low testosterone symptoms, thyroid concerns or unexplained hair shedding, you can schedule a consultation with Core Function Health to determine what evaluation may be appropriate for you.
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References
Tai T, Kochhar A. Physiology and Medical Treatments for Alopecia. Facial Plast Surg Clin North Am. 2020;28(2):149-159. PMID: 32312501
Shrivastava SB. Diffuse hair loss in an adult female: approach to diagnosis and management. Indian J Dermatol Venereol Leprol. 2009;75(1):20-27. PMID: 19172026
Owecka B, Tomaszewska A, Dobrzeniecki K, Owecki M. The Hormonal Background of Hair Loss in Non-Scarring Alopecias. Biomedicines. 2024;12(3):513. PMID: 38540126
Brough KR, Torgerson RR. Hormonal therapy in female pattern hair loss. Int J Womens Dermatol. 2017. PMID: 28492055
Farkas E, et al. Untangling estrogen therapy for menopausal hair loss: A systematic review. J Am Acad Dermatol. 2026. PMID: 42036029
Weeratian T, et al. Hair loss in athletic testosterone use in males: a narrative review. Int J Dermatol. 2025. PMID: 39572081
Kaufman KD. Finasteride, a Type 2 5alpha-reductase inhibitor, in the treatment of men with androgenetic alopecia. Expert Opin Investig Drugs. PMID: 15992088
Trost LB, Bergfeld WF, Calogeras E. The diagnosis and treatment of iron deficiency and its potential relationship to hair loss. J Am Acad Dermatol. PMID: 16635664
Bin Dayel S, et al. Is thyroid dysfunction a common cause of telogen effluvium?: A retrospective study. Medicine (Baltimore). 2024. PMID: 38181279
Herrera HO, Bordeaux JS. Risk of new-onset hair loss with semaglutide and tirzepatide: A TriNetX cohort study. J Am Acad Dermatol. 2026. PMID: 41707704
GLP-1 therapies and hair loss: A systematic review of current evidence and implications for counseling. 2026. PMID: 41998799
Glucagon-like peptide-1 receptor agonists and hair loss: A systematic review and meta-analysis. 2026. PMID: 42155605
Medical Disclaimer
This article is for educational and informational purposes only and is not intended to diagnose, treat, cure or prevent any medical condition. Hair loss has many potential causes, including conditions that may require evaluation by a dermatologist or another healthcare professional. Laboratory testing and treatment should be individualized based on medical history, symptoms, examination and clinical judgment. Do not start, stop or change medications, hormone therapy or supplements based solely on this information.