Hair Loss in Teenage Girls: Common Causes and When to See a Doctor

Why does hair loss happen in teenagers?

Hair loss feels out of place in adolescence, but the teen years are actually a common time for it. The body is navigating major hormonal shifts, nutrition is often uneven, and stress — academic, social, emotional — is high. Hair follicles are sensitive indicators of what is happening inside the body, so a variety of systemic triggers can show up as shedding before other signs appear.

The good news is that most causes in teenagers are treatable, and many reverse completely once the underlying issue is addressed [1, 2].

What are the most common causes?

Telogen effluvium is probably the most frequent culprit. A major physical or emotional stressor — a bad illness, rapid weight loss, crash dieting, a highly stressful period — pushes a large number of follicles into the resting phase at once, and they shed together two to four months later 3Ref 3Rebora A (2019).Telogen effluvium: a comprehensive review.Telogen effluvium mechanism and triggers including illness, stress, and dietary changes in teens.

Iron deficiency or low ferritin is a close second, particularly in girls with heavy periods. Low ferritin (the stored form of iron) is often missed because standard iron tests can look normal while ferritin itself is depleted. Even modest iron insufficiency is a well-recognized driver of shedding 4Ref 4Leung AKC, Lam JM, Wong AHC, Hon KL, Li X (2024).Iron Deficiency Anemia: An Updated Review.Iron deficiency as a common and often missed cause of hair shedding in teenage girls, particularly those with heavy periods.

Thyroid dysfunction — either underactive or overactive — is common enough in adolescents to be on every clinician's differential. Both states cause hair loss and are highly treatable once diagnosed 5Ref 5Jonklaas J, Bianco AC, Bauer AJ, et al. (2014).Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.Thyroid dysfunction as a treatable cause of hair loss in adolescents requiring TSH evaluation.

Hormonal imbalances, including PCOS. Polycystic ovary syndrome can present in teenagers with irregular periods, acne, increased body hair, and diffuse thinning at the crown or temples 6Ref 6American College of Obstetricians and Gynecologists (2018).ACOG Practice Bulletin No. 194: Polycystic Ovary Syndrome.PCOS as a hormonal cause of hair thinning, irregular periods, and acne in adolescents.

Alopecia areata — an autoimmune condition causing patchy, smooth bald spots — is less common but important to recognize because it has specific treatments that differ from the others 7Ref 7Dainichi T, Iwata M, Kaku Y (2024).Alopecia areata: What's new in the diagnosis and treatment with JAK inhibitors?.Alopecia areata as an autoimmune cause of patchy hair loss with specific treatment pathways including JAK inhibitors.

Traction alopecia from tight ponytails, braids, weaves, or extensions causes hair loss concentrated along the hairline or part line. It is common and often overlooked 8Ref 8Billero V, Miteva M (2018).Traction alopecia: the root of the problem.Traction alopecia from tight hairstyles as a common and often overlooked cause of hair loss concentrated along the hairline in teenage girls.

When should you see a clinician, and who?

A good first stop is a primary care clinician, who can take a history, examine the scalp, and run the key initial labs: iron and ferritin, thyroid function, and a hormonal panel if indicated.

If those come back normal or if the hair loss is patchy and does not respond to initial treatment, a dermatologist — ideally one who specializes in scalp and hair disorders — can perform a more detailed exam using a dermatoscope. You do not need to wait long before seeking care; earlier evaluation means earlier treatment and typically a better outcome 1Ref 1American Academy of Dermatology (2024).Hair Loss Resource Center.Overview of hair loss types in women including adolescents, importance of clinician evaluation.

Do not minimize concerns about disordered eating or significant psychological stress — raise these directly with the clinician. Both can drive hair loss and require their own care pathway.

What labs might a clinician order?

Depending on the history and scalp exam:

• CBC and ferritin — rules out anemia and catches low iron stores; ferritin can be low even when standard iron appears normal 4Ref 4Leung AKC, Lam JM, Wong AHC, Hon KL, Li X (2024).Iron Deficiency Anemia: An Updated Review.Iron deficiency as a common and often missed cause of hair shedding in teenage girls, particularly those with heavy periods
• TSH and free thyroid hormones — screens for both underactive and overactive thyroid states 5Ref 5Jonklaas J, Bianco AC, Bauer AJ, et al. (2014).Guidelines for the Treatment of Hypothyroidism: Prepared by the American Thyroid Association Task Force on Thyroid Hormone Replacement.Thyroid dysfunction as a treatable cause of hair loss in adolescents requiring TSH evaluation
• Hormonal panel (LH, FSH, testosterone, DHEA-S, prolactin) — evaluates for PCOS or other androgen excess 6Ref 6American College of Obstetricians and Gynecologists (2018).ACOG Practice Bulletin No. 194: Polycystic Ovary Syndrome.PCOS as a hormonal cause of hair thinning, irregular periods, and acne in adolescents
• Zinc, vitamin D, and metabolic panel — common micronutrient gaps in teens, especially those on restricted diets
• Scalp dermoscopy — a handheld tool that lets the clinician see follicle patterns, miniaturization, and any scalp inflammation up close
• Pull test — a simple bedside assessment of whether active shedding is still occurring

What can you do right now?

While waiting for an appointment:

• Loosen tight hairstyles. Tight ponytails, braids, and extensions stress the hairline and can worsen whatever is already happening 8Ref 8Billero V, Miteva M (2018).Traction alopecia: the root of the problem.Traction alopecia from tight hairstyles as a common and often overlooked cause of hair loss concentrated along the hairline in teenage girls.
• Eat consistently and include iron-rich foods — leafy greens, legumes, fortified cereals, eggs — since undernourishing the body worsens most forms of shedding.
• Avoid large-dose supplements without guidance. Excess zinc, vitamin A, and selenium can themselves cause hair loss.
• Take photos of the scalp in consistent lighting every couple of weeks. A visual record is useful to a clinician and can reveal changes the eye adapts to missing daily.
• If there is any concern about disordered eating, please raise that directly. It is relevant to care and should not be minimized.