Saunas, changing bodies, and the possibilities we discover along the way.
For years, she stayed away from saunas.
Following breast cancer surgery, during which lymph nodes had been removed from her armpit, she had been advised to avoid the heat. The concern was lymphoedema, a condition in which impaired lymphatic drainage can cause swelling.
She took the precaution seriously. Over several years, she also received regular lymphatic drainage therapy.
Today, she thoroughly enjoys saunas. Almost daily, in fact.
What changed?
Perhaps her body's capacity to manage fluid altered over time. Perhaps her confidence grew, or her understanding of the original advice changed. Perhaps several things happened, each making room for the next.
We cannot know from her experience alone. But her story invites a question that reaches beyond the sauna.
When we encounter something familiar, are we always bringing quite the same body to meet it?
Consider what happens when we step into the heat.
We may experience a sauna as a moment of relaxation, but beneath that apparent stillness, the body is remarkably busy. Blood vessels near the skin widen, circulation shifts towards the surface, the heart works harder, and sweat helps us release heat.
The temperature displayed on the wall tells us only part of the story. Our response also depends on the physiological condition we bring into the room.
And, rather unexpectedly, on the time of day.
Our bodies have their own clocks.
Core body temperature is not fixed at precisely 37°C. It follows a daily rhythm, generally reaching its lowest point towards the end of our biological night and rising towards the evening.
Even the internal temperature at which we begin sweating or increasing blood flow to the skin can shift with this rhythm.
So the same warmth encountered in the morning may not produce quite the same response as it would later in the day.
Does that make one time better than another?
Not necessarily.
The timing of passive heating may, for example, be relevant to sleep, partly because the cooling that follows helps prepare the body for rest. But a response that serves one purpose isn't necessarily preferable for every other.
We don't yet know enough to say that sauna bathing at particular times produces particular long-term health benefits.
Still, there is something intriguing about the possibility that our response to an experience might depend not only on what we encounter, but when.
And for women, biological time has another dimension.
After ovulation, rising progesterone contributes to a small increase in core body temperature, commonly around half a degree Celsius. Women who have tracked their basal temperature may recognise this change.
Less familiar is what happens to the body's cooling responses.
During the second half of the menstrual cycle, the internal temperature at which sweating and skin vasodilation begin may also rise.
It's not simply that the body's temperature changes. The temperature at which it responds can change too.
This doesn't necessarily mean that women sweat less effectively, tolerate heat differently or experience different health benefits during particular phases of their cycle. Those outcomes haven't been consistently demonstrated.
But it does raise an interesting question.
How much of what we know about heat exposure has actually been investigated in women?
Some of the most influential findings linking regular sauna bathing with cardiovascular health came from studies of Finnish men.
Women have since been included in important research, yet a 2026 review of repeated passive-heating studies found that fewer than one in three participants were women. Even when women took part, their menstrual or reproductive status was often poorly documented.
And only 17 participants were explicitly identified as postmenopausal in the review's reported categories.
That doesn't mean there were only 17 postmenopausal women. It means the researchers often hadn't been given the information needed to know.
Which is rather remarkable when we consider how profoundly reproductive hormones can influence temperature regulation.
Take the menopausal hot flush.
A sudden rush of warmth, flushed skin, perspiration—sometimes in the middle of the night, when nothing in the surrounding room seems to have changed.
Why does it happen?
Deep within the brain, the hypothalamus helps coordinate our responses to temperature. Among its intricate networks are nerve cells known as KNDy neurons, whose activity is influenced by oestrogen.
As oestrogen signalling changes during the menopausal transition, these neurons can become more active, influencing the pathways that trigger heat loss.
Blood vessels near the skin dilate. Sweating begins. The body launches a cooling response, even though the surrounding air may be no warmer and core temperature may have changed very little.
The precise mechanisms are still being investigated, but the distinction is fascinating.
Feeling hotter, being hotter, and responding to heat are not necessarily the same thing.
Our experience of warmth depends partly on how the body interprets and regulates temperature.
And that relationship changes through life.
But not every change is governed by hormones or the passing of years. Some arise from experience itself.
Someone accustomed to regular sauna bathing may respond differently from someone entering the heat for the first time.
Repeated heat exposure can lead to measurable adaptations. Cardiovascular strain during a comparable exposure may lessen. Blood volume and sweating responses can change, helping the body manage the demands of heat.
But experience isn't the only difference we bring into the room. Body composition matters too. Fat and muscle have different thermal properties, and women, on average, carry a higher proportion of body fat than men. Alongside differences in body size and surface area, this can influence how heat is exchanged and experienced.
These variations don't mean that one sex is necessarily better equipped for the sauna than the other. Nor does finding the heat uncomfortable mean we're responding badly to it.
Perhaps that's worth remembering when sauna bathing becomes a competition over who can remain longest in the fiercest heat. Biology doesn't award medals for discomfort.
But there is another, less obvious part of the experience.
What happens after we leave?
We might imagine that the body's work is almost finished. Heart rate begins to settle, the skin cools, and gradually we return to a familiar sense of comfort.
Yet different biological processes don't necessarily finish responding at the same time.
In one small human experiment, researchers examined gene activity in circulating immune cells before, immediately after and an hour following sauna exposure.
Some changes became more pronounced during recovery, after the heat exposure had ended.
Other experiments involving heated muscle have found that certain heat-shock responses continue developing after the heating itself is over.
These molecular changes don't automatically translate into health benefits. But they reveal something easily overlooked.
Leaving the heat is not necessarily the end of the body's response to it.
Some adjustments happen within minutes. Others unfold over hours. With repeated exposure, adaptations can develop over days and weeks.
The body carries something of the encounter forward.
And that makes me think again of the woman who once stayed away from saunas.
These days, she visits almost daily. The warmth has become a familiar pleasure, one she might once have imagined was behind her.
What changed in the intervening years? Perhaps more than we can ever measure.
And perhaps that's worth remembering beyond the sauna, too. When something familiar feels different, it isn't always the world around us that has changed.
Sometimes, it's the body we've brought to meet it.
References
- Stephenson LA, et al. Circadian rhythm in sweating and cutaneous blood flow. American Journal of Physiology. 1984.
- Haghayegh S, et al. Before-bedtime passive body heating by warm shower or bath to improve sleep: a systematic review and meta-analysis. Sleep Medicine Reviews. 2019.
- Baker FC, et al. Temperature regulation in women: effects of the menstrual cycle. Temperature. 2020.
- Laukkanen T, et al. Association between sauna bathing and fatal cardiovascular and all-cause mortality events. JAMA Internal Medicine. 2015.
- Mee JA, et al. Passive heat intervention research in women: systematic review and audit of female representation. Experimental Physiology. 2026.
- Gombert-Labedens M, et al. Effects of menopause on temperature regulation. Temperature. 2025.
- Bouchama A, et al. A model of exposure to extreme environmental heat uncovers the human transcriptome to heat stress. Scientific Reports. 2017.
- Gibson OR, et al. Skeletal muscle angiogenic, regulatory, and heat shock protein responses to prolonged passive hyperthermia of the human lower limb. American Journal of Physiology – Regulatory, Integrative and Comparative Physiology. 2023.
- Cramer MN, et al. Human temperature regulation under heat stress in health, disease, and injury. Physiological Reviews. 2022.
