Hair cortisol results explained: what your number means

A hair cortisol result tells you how much cortisol was stored in your hair sample, given in picograms of cortisol per milligram of hair (pg/mg). It reflects your average cortisol over the months that hair took to grow, usually about the last three, and it is shown against the reference range of the laboratory that measured it.¹ The most important thing to know is that the range belongs to that laboratory. Healthy values differ more than tenfold between methods, so a number that is high on one report can be low on another.²³ This guide explains what the number means, what high and low results can reflect, what else can move them, and when to see a doctor.

What the number on your report means

A picogram is a millionth of a microgram, so these are tiny amounts. Some laboratories and papers use nanograms per gram (ng/g) instead. The number is identical, because 1 ng/g equals 1 pg/mg.³ Some reports also give cortisone, a closely related, inactive form of cortisol. In one study of Cushing's syndrome, hair cortisone was slightly more accurate than hair cortisol at identifying the condition.⁴

The result covers a period, not a moment. Hair grows 0.6 to 1.4 cm a month, so a standard 3 cm sample spans roughly two to five months, about three on average.¹ It also stops short of the day you cut it: the centimetre nearest the scalp reflects hair formed about 1.3 to 2.2 months earlier.⁵ So a result describes, roughly, a three-month stretch that ended a month or more before you took the sample. How hair cortisol testing works explains the science, and the hair sample calculator shows which months your sample covers.

Why there is no single normal range

Different laboratory methods give very different numbers for similar people. These are values from four published studies of adults:

The whole LC-MS/MS range sits below the bottom of the early immunoassay range. Even laboratories using the same broad method differ: four laboratories using different ELISA kits reported healthy values up to 2.3-fold apart.⁸ The first international comparison of laboratories found that methods rank samples in much the same order but proposed correction factors to convert between them, and a 2025 systematic review found that collection procedures and average values varied significantly across studies.⁹¹⁰ Sex matters as well: in the Whitehall II study, women's hair cortisol was 17.0 per cent lower than men's.¹¹

So treat any "normal hair cortisol level" you see quoted, including the figures above, as specific to one laboratory, method and population. The Fortuna study is one of the few to set a formal reference interval, following the clinical laboratory standard for doing so (CLSI EP28-A3c), and even that range applies to its own method and the people it studied.²

What a high result can reflect

A result above your laboratory's range means your body was exposed to more cortisol than most of the reference group over the months the hair covers. On its own, it does not say why. In research, higher hair cortisol has been linked with:

• Ongoing stress. Groups under chronic stress had 22 per cent higher hair cortisol, and 43 per cent higher when the stress was still continuing.¹²
• Shift work. In one study shift workers had 47.32 pg/mg against 29.72 pg/mg in day workers, although the difference was confined to younger workers.¹³
• Weight. In one study, people with obesity had 30.8 pg/mg against 8.4 pg/mg in people of normal weight.¹⁴
• Pregnancy. In new mothers, hair that grew during the third trimester had twice the cortisol of hair from a control group.¹⁵
• Hydrocortisone. In people taking hydrocortisone tablets, hair cortisol rises with the dose.¹⁶

Very high results are seen in Cushing's syndrome. In one study, patients had a geometric mean of 106.9 pg/mg against 8.4 pg/mg in healthy controls measured by the same laboratory.⁶ But Cushing's syndrome is rare, with two to three new cases per million people a year in European studies, and a high hair result cannot diagnose it.¹⁷ Nor can hair cortisol diagnose depression, anxiety or burnout: a meta-analysis found no consistent link with mood disorders, and a 2026 review found no biological marker reliable enough to diagnose burnout.¹²¹⁸

What a low result can reflect

A result below the range means less cortisol exposure than most of the reference group. Lower hair cortisol has been found in:

• people with post-traumatic stress disorder (PTSD), 59 per cent lower in one study, and with anxiety disorders, 17 per cent lower across a meta-analysis¹⁹¹²
• workers with a long-running imbalance between the effort they put in and the rewards they got, in a study that followed them over time²⁰
• people using inhaled, nasal or skin corticosteroids, whose hair cortisone was lower (6.8 against 8.5 pg/mg), a sign of subtle suppression of the body's own production²¹

Low results can also come from the hair rather than the body, because dye, heat treatments, sunlight and long storage all lower measured values (see the next section). A low hair result does not diagnose adrenal insufficiency, including Addison's disease. That is diagnosed with blood tests, the standard being the short Synacthen test.²²

What can shift a result without changing your cortisol

Some factors change the cortisol measured in the hair, not the cortisol in your body:

• Hair dye and heat treatments. People who dyed their hair had 12.5 per cent lower values in the Whitehall II study, and heat treatments were linked with lower values in a South London study.¹¹²³
• Sunlight. 40 hours of natural sunlight lowered hair cortisol by a median of 54 per cent in an experiment.²⁴
• Washing. More frequent washing is linked with lower values, mostly in hair further from the scalp.²⁵²⁶
• Season. In a systematic review, 76 per cent of studies found differences between seasons.²⁷
• Storage. Cortisol declines slowly in stored hair, and researchers recommend analysis within three to six months.²⁸
• Steroid medicines. Depending on the drug, these can raise or lower the result.¹¹²¹

The details, and how to take a fair sample if you colour or style your hair, are in testing dyed or treated hair.

Comparing with your own earlier results

Because laboratory ranges differ so much, your own previous results are often the most useful comparison, and hair suits this well. The same people's hair cortisol correlated at r = 0.84 from one month to the next in one study, and a stable personal component explained 59 to 82 per cent of the variation over months in another.²⁹³⁰ For a fair comparison:

• use the same laboratory and method each time
• take the sample from the same place, the back of the head just below the crown, where results vary least³
• keep hair treatments the same, or note any change
• test at a similar time of year if you can²⁷
• post each sample promptly²⁸

Small differences mean little: with one LC-MS/MS method, variation within the same person was below 15 per cent.³¹ Larger, sustained changes carry more weight. For a sense of scale, hair cortisol fell over the first three to six months of a meditation training programme, and by 44 per cent within a group of shift-working nurses after online insomnia therapy.³²³³ Because each sample covers about three months, retesting much sooner than that mostly measures the same stretch of time again; see how often to test cortisol.

When to see a doctor

See a doctor if you have symptoms that could mean an adrenal condition, whatever your hair result says. Signs of too much cortisol include more fat on the neck, upper back and tummy with thin-looking arms and legs, a red, round face, easy bruising, stretch marks and weakness at the tops of the arms and legs.³⁴ Signs of too little include extreme tiredness, darker patches of skin, weight loss, dizziness on standing and craving salt.³⁵

A result well above or below your laboratory's range is also worth discussing, especially if it is unexpected. Take the report with you, with details of any hair treatments and steroid medicines. A doctor who suspects Cushing's syndrome will arrange late-night saliva, 24-hour urine or dexamethasone suppression tests; one who suspects adrenal insufficiency will arrange blood tests, including a Synacthen test.¹⁷²² Hair cortisol is not part of either guideline. Our guides to high cortisol symptoms and low cortisol symptoms have more detail.