Why you feel too hot or too cold during your period
One minute you're throwing off the covers at 3am, flushed and overheated. The next you're shivering and reaching for an extra layer in a room that hasn't changed temperature at all. Or maybe you just feel permanently off — a vague feverish heaviness that isn't quite a fever, combined with chills that don't quite make sense. Welcome to what many women call the "period flu" — and while it might feel like your body has completely lost the plot on temperature, there is a precise biological explanation for every degree of it.
The two hormones running your internal thermostat
Your body temperature is not simply a response to the environment. It is actively regulated by your hormones — specifically estrogen and progesterone, which have opposite and measurable effects on your body's thermoregulation system throughout the cycle.
Estrogen
Estrogen promotes heat dissipation — it enhances vasodilation (widening of blood vessels) and supports sweating responses, helping the body shed heat efficiently. When estrogen is high in the follicular phase, body temperature is at its lowest and most stable.2
Progesterone
Progesterone raises the hypothalamic thermoregulatory set point — essentially turning up the body's internal thermostat. It also promotes vasoconstriction in the skin, reducing heat loss. The result is a measurably higher core temperature throughout the luteal phase.3
How temperature shifts across your cycle
The temperature rise begins after ovulation — when progesterone takes over from estrogen as the dominant hormone — and remains elevated until menstruation begins. Once the period starts and progesterone drops, body temperature falls back to its follicular baseline. This is why basal body temperature tracking has been used for decades as a method of confirming ovulation: the rise of 0.3–0.7°C is reliable and consistent.1
Why you feel hot and cold at the same time
The paradox of feeling simultaneously too hot and too cold is one of the strangest aspects of the premenstrual and menstrual experience — and it has a precise explanation. When progesterone drops sharply before the period, the hypothalamic thermostat destabilizes. The body's internal temperature regulation becomes temporarily erratic — oscillating between heat retention and heat dissipation in a way that produces sudden flushes of warmth followed by chills, often within the same hour.
At the same time, prostaglandins released as the uterine lining breaks down can produce fever-like sensations — not an actual fever, but the same neurological signals that make you feel feverish: body aches, heaviness, fatigue, and temperature dysregulation. Combined with the hormonal instability, this creates the full "period flu" experience that so many women describe but rarely have explained to them.4
A comprehensive review published in PubMed confirmed that estrogens promote lower body temperatures through augmentation of heat dissipation responses, while progesterone promotes higher body temperatures through both centrally regulated changes in thermoregulatory set-point and peripheral effects including augmented vasoconstriction in the skin. These are well-established, measurable, reproducible hormonal effects — not subjective experience.2
The specific sensations — and what's driving each one
Night sweats
Elevated body temperature from progesterone disrupts the cooling the body needs for deep sleep — producing night sweats as it attempts to regulate.1
Chills
When progesterone drops before the period, the thermostat destabilizes. Chills are the body's attempt to generate heat when it perceives its temperature as too low.4
Feverish feeling
Prostaglandins mimic the neurological signals of fever — aching, heaviness, and temperature sensitivity — without producing an actual fever.4
Hot flushes
Falling estrogen before the period affects the hypothalamus in a similar way to menopause — triggering brief episodes of intense warmth and flushing.3
Achy body
Prostaglandin-driven inflammation combined with temperature dysregulation creates the same full-body achiness associated with mild fever or flu.4
Feeling "off"
The combination of hormonal withdrawal, temperature instability, prostaglandin inflammation, and disrupted sleep creates a pervasive sense of unwellness that's hard to pinpoint but completely real.3
Iron loss can make you feel colder
There's an additional driver of cold sensitivity during menstruation that is often overlooked: iron loss. Blood loss during the period reduces iron stores — and iron is essential for thermoregulation and circulation. Women with heavier periods may notice they feel significantly colder during menstruation specifically because their iron and haemoglobin levels are temporarily lower, reducing the blood's ability to carry oxygen and regulate heat effectively.5 If you regularly feel very cold specifically during your period, this is worth considering alongside the hormonal picture.
What helps
Cool your bedroom for the luteal phase
Since progesterone raises body temperature throughout the luteal phase and disrupts nighttime cooling, keeping your bedroom cooler than usual in the 10 days before your period directly counteracts the hormonal thermostat effect and improves sleep quality.
Layer for the chills
The temperature oscillations of the premenstrual and menstrual days respond well to layering — clothes and bedding you can add or remove quickly — rather than trying to find a fixed temperature that works for both the hot and cold episodes.
Stay well hydrated
Dehydration worsens temperature regulation at any time of the month — and during menstruation, when the body is losing fluid and iron, staying hydrated directly supports the body's ability to regulate its temperature more effectively.
Support iron during your period
If you regularly feel very cold during menstruation, eating iron-rich foods — leafy greens, legumes, meat — in the days before and during your period supports your body's thermoregulation capacity by maintaining haemoglobin levels.5
When does it resolve?
The temperature dysregulation of the premenstrual and menstrual days resolves reliably within the first few days of the period beginning. As progesterone drops to its lowest point and estrogen begins rising in the new cycle, the thermoregulatory set point returns to its follicular baseline. The night sweats ease, the chills settle, and the feverish heaviness of the period flu lifts. Not because you've recovered from an illness — but because the hormonal environment driving the symptoms has shifted, and your body's internal thermostat has recalibrated.
Temperature changes, fatigue, chills — they all follow your cycle. Feelings shows you your phase so every physical symptom comes with context. Log your symptoms and stop wondering what your body is doing.
References
- Morel, C., et al. (2020). Temperature regulation in women: effects of the menstrual cycle. Temperature / PubMed. PubMed
- Charkoudian, N. & Stachenfeld, N. (2016). Sex hormone effects on autonomic mechanisms of thermoregulation in humans. PubMed. PubMed
- Stachenfeld, N.S. & Taylor, H.S. (2022). Influences of ovarian hormones on physiological responses to cold in women. PMC. PMC
- Nua Woman. (2026). Period flu explained: understanding body temperature change during your period. Nua Woman
- Embrace Comfort. (2024). Beyond the thermometer: how hormones drive temperature variations during menstruation. Embrace Comfort
- Hessemer, V. & Brück, K. (1985). Thermoregulatory responses to cold transients: effects of menstrual cycle in resting women. PubMed. PubMed