Flat morning
- Healthy population range
- Your possible rhythm
Little rise in the 30 minutes after waking.
Slow starts. Hours and caffeine to come online.
12 tests · 4 weeks $99 on subscription
Start Protocol NowProtocol SP-28 · single-subject design
Four weeks. Twelve saliva tests. One dose held constant. See whether your body is actually adapting — or whether you’ve just built a habit.
12 tests. $99 on subscription, $139 one-time.
It should peak within about 30 minutes of waking, fall through the day, and bottom out at night.
When people say their cortisol feels off, they almost never mean the level. They mean the shape. And a single reading — at an unknown time, on an unknown day — tells you nothing about shape.
Little rise in the 30 minutes after waking.
Slow starts. Hours and caffeine to come online.
Doesn’t come down at night.
Tired but wired. Second wind at 10pm.
Small gap between morning and evening.
Same energy all day — never sharp, never off.
Big spike to a stressor, long return.
Small things land hard. Takes ages to settle.
These are shapes, not diagnoses. What matters is which one is yours, and whether it moves. The dotted line is a typical curve for comparison.
Not what you’ve been told.
A single Finnish sauna session can raise cortisol, not lower it — and the rise is smaller in people who are already heat-adapted.Pilch et al., Journal of Human Kinetics, 2013
The direction depends entirely on when you measure. Cortisol dips during the bath, then peaks about 15 minutes after you step out.Jezová et al., Acta Physiologica Scandinavica, 1994
+96%
Minute 30 · session 1 — Peak, about 15 min after you step out
In women new to sauna, cortisol nearly doubled after the first session — and rose noticeably less by the seventh, two weeks later.Pilch et al., Journal of Human Kinetics, 2003
In 40 female athletes tracked over six weeks with saliva samples, the same pattern: the response shrank as the weeks went on.Ahokas et al., Temperature, 2025 — study funded by Harvia, a sauna manufacturer
That shrinking response is the most reproducible finding in this literature. It’s your body getting efficient at a stressor it now recognises.
And it’s completely invisible if you measure once.
You are the subject and the control. The experiment only works if exactly one thing changes.
Your daily rhythm is bigger than anything sauna does to it. Morning one day and evening the next means you’re measuring the clock, not the sauna.
10–20 minutes, 80–90 °C dry or 50 °C infrared, three to four times a week. Hold it — don’t increase it because it starts feeling easy. That feeling is the adaptation.
No new supplement, no new sleep schedule, no new training block. One variable, or no answer.
Not during. Not at the door. Cortisol peaks after you leave — sample early and you read the wrong part of the curve.
Nothing. Normal life. No sessions this week.
Three tests — waking, +30 min, evening.
Your starting shape.
Protocol begins. Three to four sessions at your fixed dose.
Two tests — before a session, then 20–40 min after.
Your unadapted response.
Same dose. Change nothing.
Two tests — before and after a session.
The first sign of drift.
Same dose, then one rest day. Close the loop.
Two tests around a session, plus three on a rest day.
Response trajectory, and your closing curve.
Twelve tests. Three of them measure your response on three different weeks — that’s a trajectory, not a before-and-after.
Does the gap between your before and after readings get smaller from week 2 to week 4?
If it does, your stress response has adapted to this stimulus. This is the documented pattern — it’s what the sauna literature has shown since 1986.
Then compare your week 1 curve to your week 4 curve. Did the gap between morning and evening widen? Did the evening reading come down?
No published study has ever measured this for sauna. The research measures the response around a session — not whether the daily curve itself changes over weeks.
You’re not reading someone else’s result. You’re generating your own.
That’s a result too. Either the dose was too light, four weeks is too short for your rate of adaptation, or this stimulus does little for you specifically — response to heat varies substantially between individuals.Brazaitis et al., PLOS ONE, 2014
All three are worth knowing. None of them were knowable before you measured.
Twelve tests, delivered every four weeks. Run the protocol again at a new dose.
Start the protocolWhy it repeats: once your response has flattened, the stimulus isn’t a stimulus anymore. The next question isn’t is it working — it’s what happens if I change the dose. New dose, new four weeks, new measurement.
The sauna literature is small: most studies have fewer than 40 participants, protocols vary widely in temperature, duration and frequency, and the direction of the acute cortisol effect genuinely conflicts between studies. The strongest and most consistent finding is that the acute response diminishes with repeated exposure. No study has measured whether sauna changes the shape of the daily cortisol curve. The Hormometer measures cortisol; it does not change it.
Talk to a doctor first if you have a known heart condition or arrhythmia, uncontrolled high blood pressure, or if you’re pregnant.
Hydrate. Twenty minutes maximum per session. Get out if you feel lightheaded.
Regular high-heat exposure temporarily lowers sperm count and motility. It reverses — but it’s worth knowing if you’re trying to conceive.Garolla et al., Human Reproduction, 2013