The hair growth cycle — why hormones matter so much
Every hair is in one of three phases: anagen (growth, two to six years), catagen (transition, two to three weeks) and telogen (resting and shedding, two to three months). Approximately 85 to 90 percent should be in anagen at any time. When hormonal disruption occurs, an abnormal number shift into telogen simultaneously — producing the diffuse shedding women notice two to three months after the hormonal event that triggered it.
This two to three month lag explains why hormonal hair loss is so often mysterious. Postpartum shedding appears two to three months after delivery. Post-pill shedding appears two to three months after stopping. Stress-related shedding appears two to three months after the stressful period. The visible symptom is chronologically disconnected from its hormonal cause.
The most overlooked cause — ferritin, not haemoglobin
Ferritin — the iron storage protein — is the most consistently overlooked cause of hair loss in women who train and menstruate. Standard blood panels measure haemoglobin. Ferritin is a separate test that must be specifically requested.
Hair loss research consistently shows hair follicle function is impaired at ferritin levels below 70 mcg/L — a level most laboratories consider normal. A woman with ferritin of 35 mcg/L receives a normal result from her GP and loses significant hair specifically because of that ferritin level. Active women who menstruate and train without specific iron attention frequently operate well below this threshold.
Source: Rushton et al., Causes of hair loss and the developments in hair rejuvenation — PubMed.
Testing, causes and what to do — the practical guide
Test specifically: Ferritin above 70 mcg/L. Full thyroid panel including antibodies — subclinical hypothyroidism produces hair loss before other symptoms. Oestradiol and FSH on days 2 to 5 of the cycle. Testosterone and SHBG. Zinc. Vitamin D. B12. These cover the seven most common hormonal and nutritional causes.
Androgenic alopecia — pattern thinning at the temples and crown with hairline intact — is driven by DHT sensitivity rather than elevated testosterone levels. A dermatologist or trichologist referral is appropriate for this specific pattern.
Thyroid hair loss produces diffuse thinning alongside other thyroid symptoms — fatigue, weight changes, cold intolerance. A full thyroid panel including antibodies identifies this before TSH alone becomes abnormal. Read the complete guide at thyroid and your menstrual cycle.
The recovery timeline: Address the cause. Wait two to three months for shedding to stop. Wait another three to six months for visible regrowth. Full density takes six to twelve months. Every woman who has tried supplements for four weeks and seen no result has not given the hair cycle enough time to respond.
The complete supplement protocol — phase-specific iron replenishment, zinc, vitamin D and the nutritional framework that supports hormonal and hair health — is in The Women's Hormone Blueprint.