A blood test sees one morning. Your hair has kept the last three months.
Cortisol rises and falls all day, so blood, saliva and urine tests only tell you about the moment they were taken. Hair grows about a centimetre a month and stores cortisol as it grows, so one small sample shows your average over roughly the past three months. That makes a hair test the most accurate way to measure your long-term cortisol from a single sample, and far more consistent from one test to the next.
- 6 months back6 mo
- 5 months back5 mo
- 4 months back4 mo
- 3 months back3 mo
- 2 months back2 mo
- Last month1 mo
A blood or saliva test One moment, today. On this scale it is thinner than the line marking your scalp.
Why hair tells you more
Every cortisol test answers a different question. Blood and saliva ask what your cortisol is doing now. Hair asks where it has been. For tiredness, sleep, weight or stress that has lasted months, that is the question that matters.
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One bad morning cannot skew it
A tense journey, a poor night or the needle itself can push a blood or saliva result up. In a three-month average, one day is about one ninetieth of the result.
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No timing rules
Blood is usually taken before 9 or 10am, saliva at set times, and urine for a full 24 hours. A hair sample can be cut whenever suits you.
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One sample instead of many
Most of the variation in a single saliva sample reflects that day, so studies need samples on several days just to describe a typical week. Hair has been collecting the whole time.
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It is consistent
The same person's hair cortisol correlates strongly from one month to the next, far more closely than repeated saliva or urine results. That consistency is what lets you test again later and see whether sleep, work or treatment has moved your levels.
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It is easy to do at home
No needles, no clinic and nothing to keep cold. Cut, seal and post.
Hair, blood, saliva and urine compared
Hair wins on every question about long-term cortisol. Doctors still diagnose adrenal disease with blood, saliva and urine tests, and we show that too.
| Feature | Hair | Blood | Saliva | 24-hour urine |
|---|---|---|---|---|
| What it measures | YesAverage cortisol over roughly three months | NoCortisol at the moment of the draw | NoFree cortisol at each moment you spit | PartlyTotal free cortisol passed in one day |
| Unaffected by a stressful morning | YesOne bad day is a tiny part of 90 | NoA tense journey or the needle itself can raise it | NoReflects the hour you collect | PartlySmooths out hours, not days |
| No timing rules | YesCut the sample whenever suits you | NoUsually before 9 or 10am | NoSet times, often late at night or on waking | NoCollect every pass of urine for 24 hours |
| No needles | Yes | NoVein or finger-prick | Yes | Yes |
| Consistent from one test to the next | YesMonth-to-month results correlate strongly | NoVaries with time, stress and the needle | NoMost of a single result reflects that day | PartlyVaries a lot from day to day |
| Shows a long-term pattern from one sample | YesCan be split month by month | NoNeeds repeat draws | NoNeeds many collection days | NoNeeds repeat collections |
| Used by doctors to diagnose adrenal disease | NoNot yet in guidelines; promising in research | YesMorning cortisol, Synacthen and suppression tests | YesLate-night saliva for Cushing's | YesA first-line test for Cushing's |
How a hair cortisol test works
- A kit arrives by postWith instructions, foil or a card to hold the hair, and an envelope.
- Cut a small sampleA small lock, 2 to 3 mm thick, from the back of your head, cut as close to the scalp as you can.
- Post it backHair needs no fridge or freezer. Seal it in the envelope and post it promptly.
- Read your resultsThe laboratory measures the cortisol and reports your average over about the last three months.
Hair cortisol tests are sold direct as home kits; you do not need a doctor's referral. Our guide to the hair cortisol test covers accuracy, sampling and results, and cortisol tests compared lists where to get one, alongside blood, saliva and urine tests.
Start here
All 45 guidesHair cortisol testing
All 14- The hair cortisol testHow hair records cortisol, what the research shows about accuracy, how to take a sample and what a hair test is not for.
- Is hair cortisol testing accurate?How hair cortisol compares with repeated saliva and urine, how consistent it is, its accuracy for Cushing's and where it falls short.
- Hair vs blood cortisol testBlood shows one moment, hair shows months. Timing, the needle, the pill and lab methods compared, and when blood is the right test.
- How to take a hair sampleWhere to cut, how much to take, why the cut must be close to the scalp, and the common mistakes to avoid.
- Hair cortisol results explainedWhat pg/mg means, why ranges differ between laboratories, what high or low results can reflect and when to see a doctor.
Understanding cortisol
All 11- What is cortisol?What cortisol does, how the HPA axis and ACTH control it, free and bound cortisol, and the four ways to measure it.
- Normal cortisol levelsTypical ranges for blood, saliva, urine and hair cortisol, the NICE thresholds for low cortisol, and why your own lab's range counts.
- Cortisol daily rhythmThe daily cortisol curve, the awakening response, sleep loss, shift work and why timing matters for every test except hair.
- Cortisol and stressHow acute and chronic stress change cortisol, what hair studies show, and why how stressed you feel and your cortisol often differ.
- How to lower cortisolMeditation, exercise, sleep, alcohol and diet: what lowers cortisol in trials, what is unproven, and how to check it is working.
Symptoms and conditions
All 7- High cortisol symptomsThe signs of too much cortisol, the most common causes, everyday rises that are normal, and when symptoms need a doctor.
- Low cortisol symptomsThe signs of low cortisol, its causes including stopping steroids, what an adrenal crisis looks like and how doctors diagnose it.
- Testing for Cushing's syndromeThe first-line tests for Cushing's syndrome, their cut-offs, why they are repeated, and what research on hair cortisol shows.
- Testing for Addison's diseaseHow Addison's disease is diagnosed with morning cortisol and Synacthen tests, adrenal crisis and sick-day rules, and why hair cannot help.
- Burnout and cortisolWhat studies of hair cortisol show about burnout, work stress and shift work, why no test diagnoses burnout, and what can help.
Where to get a cortisol test
Tests you can order yourself, by the kind of sample. The span under each heading is how much time that sample covers.
Hair
Average over about three months
Blood
One moment, usually a morning
Saliva
One to four moments in a day
24-hour urine
One day's total
Dried urine
Four or five moments in a day
Prices as shown on each provider's website when we last checked; see cortisol tests compared for collection details. Links to other providers are unpaid; we may benefit from links to Cortigenix.
Cortisol tools
When you need a doctor's test instead
If you have signs of Cushing's syndrome or adrenal insufficiency, such as unexplained weight loss, dizziness on standing, darkening skin, purple stretch marks or easy bruising, see a doctor. These conditions are diagnosed with blood, saliva and urine tests, often with a medicine given first to see how your adrenal glands respond.
Hair testing is not yet part of the diagnostic guidelines. In research it has detected Cushing's syndrome with accuracy similar to the standard first tests, and it can look back over months in cases where cortisol comes and goes. It is not a way to rule a condition in or out on your own.
- Testing for Cushing's syndromeThe first-line tests for Cushing's syndrome, their cut-offs, why they are repeated, and what research on hair cortisol shows.
- Testing for Addison's diseaseHow Addison's disease is diagnosed with morning cortisol and Synacthen tests, adrenal crisis and sick-day rules, and why hair cannot help.
- The blood cortisol testHow a morning blood cortisol test works, how to prepare, typical ranges and NICE thresholds, and what can skew the result.
- The saliva cortisol testDaily profiles, the waking rise and the late-night test for Cushing's: how saliva testing works, how to collect and what spoils a result.
- The 24-hour urine cortisol testHow to collect a 24-hour urine sample, what urinary free cortisol shows, typical ranges, and why doctors ask for more than one.
- Getting a cortisol test from your doctorWhen doctors test cortisol, which tests they use, how to prepare, what to ask and what happens after the result.
Common questions
What is a hair cortisol test?
A laboratory test that measures the cortisol stored in a small sample of hair cut close to the scalp. Hair grows about a centimetre a month and takes up cortisol from the blood as it grows, so the 3 cm nearest the scalp gives an average of roughly the last three months.
Is a hair cortisol test more accurate than a blood test?
For measuring your long-term cortisol, yes. A blood test measures cortisol at the moment the needle goes in, and cortisol changes through the day and with stress, food, exercise, sleep and even the needle itself. A hair test reflects the average over months, which is what most people mean when they ask whether their cortisol is high or low, and the same person's result is far more consistent from one test to the next.
For diagnosing Cushing's syndrome or adrenal insufficiency, doctors still use blood, saliva and urine tests, including dynamic tests such as the Synacthen test. A hair test does not replace those.
How much does a hair cortisol test cost?
The Cortigenix hair test costs £126.75 on cortigenix.com (checked 20 October 2026), including the kit, return postage in the UK, laboratory analysis and your results. Single-moment blood and saliva tests usually cost less per test, but you would need many of them to estimate a three-month average.
How long does hair need to be?
Each centimetre covers about a month, and most laboratories test the 3 cm nearest the scalp. Cortigenix asks for at least 1 cm, cut as close to the scalp as possible from the back of the head, about 2 to 3 mm thick. Body hair is not a reliable substitute, so if your head hair is very short, ask the laboratory before ordering.
Does hair dye affect a hair cortisol test?
It can. Studies have found somewhat lower hair cortisol in people who dye their hair or use heat treatments, and long exposure to sunlight lowers it too. Washing mainly affects hair further from the scalp. The newest hair is the least affected, which is why samples are cut as close to the scalp as possible. Tell the laboratory about any treatments.
Can I test my cortisol at home?
Yes. You can cut a hair sample at home and post it, collect saliva samples at set times, collect urine for 24 hours, or take a finger-prick blood sample. Only the hair test gives a long-term average from one sample with no timing rules.