Have You Experienced...
- Diffuse thinning across the scalp without classic male or female pattern
- Hair shedding that started after illness, stress, pregnancy, or a move
- Brittle hair, slow growth, brittle or ridged nails
- Eyebrow thinning, especially the outer third
- Normal "thyroid" labs but classic hypothyroid hair texture
- Worsening despite biotin, minoxidil, or topical treatment
- Hair loss alongside fatigue, weight changes, or cold intolerance
- More hair than usual in the shower or on the pillow
Quick Answer
Hair is one of the body's first systems to express systemic stress. Diffuse thinning typically points to thyroid dysfunction (often with normal TSH), heavy metal accumulation (mercury, arsenic), nutrient depletion (especially ferritin under 70), or chronic inflammatory load from mold, infection, or autoimmune disease. Treating with topicals alone misses every one of these. The hair returns when the underlying systemic issue is corrected — usually within 4–9 months.
The Real Causes of Diffuse Hair Thinning
Thyroid dysfunction
Even subclinical hypothyroidism — normal TSH but low free T3 or elevated reverse T3 — drives hair thinning. Standard screening misses these patterns. More on hormones →
Heavy metals
Mercury, arsenic, and thallium disrupt the hair follicle directly. Hair tissue mineral analysis often catches this when blood metal levels look normal. More on metals →
Iron / ferritin depletion
Ferritin under 70 ng/mL is associated with telogen effluvium even when hemoglobin is "normal." The follicle is highly iron-dependent.
Chronic inflammation (CIRS)
Mold illness suppresses the anagen growth phase. Mast cell activation does the same. Both produce diffuse thinning with no scalp inflammation visible.
Nutrient depletion
Zinc, B12, folate, vitamin D — each is essential for hair production. Often depleted in patients with gut dysfunction or restricted diets.
HPA-axis dysregulation
Sustained cortisol pushes follicles into the telogen (resting) phase prematurely. Common after acute illness or prolonged stress — the "three months later, hair started falling out" pattern.
Topicals not working?
The cause of hair thinning is rarely on the scalp. Our 10-minute assessment maps your pattern.
Testing
- Full thyroid panel — TSH, free T3, free T4, reverse T3, TPO and thyroglobulin antibodies
- Ferritin and iron studies — ferritin target above 70 ng/mL for hair
- Hair tissue mineral analysis (HTMA) — long-term mineral and metal exposure pattern
- Mycotoxin urine panel if mold exposure history is present
- Comprehensive nutrient panel — zinc, B12, folate, vitamin D, biotin
- Diurnal cortisol in patients with stress-onset shedding
- Sex hormone panel (DUTCH) — DHT and androgen metabolism for pattern hair loss
Frequently Asked Questions
In women, the most common causes we find are low ferritin (under 70 ng/mL despite normal hemoglobin) and subclinical thyroid dysfunction (normal TSH but low free T3 or elevated reverse T3). In patients with broader systemic symptoms, mold illness and heavy metal load become more likely. Most patients carrying a "telogen effluvium" diagnosis have one of these unaddressed.
Yes — diffuse, non-scarring hair loss is reversible when the underlying systemic cause is corrected. Most patients see regrowth within 4–9 months of addressing the root cause. Topical and follicle treatments help the cosmetic picture but don't change the trajectory if the systemic driver is still active.
Biotin deficiency is rarely the actual cause of hair loss in adults. Supplementing biotin can falsely elevate or suppress thyroid lab results — which sometimes masks the very thyroid pattern driving the hair loss. We typically have patients stop biotin for 72 hours before thyroid testing.