It starts as a pressure somewhere in the chest or neck. Then heat climbs up into your face, your skin flushes, and within a minute you are peeling off layers in a room where everyone else is comfortable. Two minutes later you are cold and damp.
At night it is worse. You wake soaked, change the pillowcase, and lie there wide awake at 3am.
Hot flashes and night sweats are the most common symptom of the menopause transition. Most people who go through it will have them at some point. They are also the symptom with the best evidence behind the treatments, which is the good news buried in this piece.
This covers what happens in the body during a flash, how long they tend to last, the triggers worth testing, what helps and what does not, and when a sweat deserves a different explanation.
It is general information and not medical advice. Decisions about treatment belong in a conversation with a clinician who knows your history.
What a Hot Flash Actually Is
Your brain keeps your core temperature inside a narrow comfortable band. The hypothalamus, a small region at the base of the brain, acts as the thermostat. As long as your temperature stays inside the band, it does nothing.
In perimenopause, falling and fluctuating oestrogen changes how a group of neurons in the hypothalamus behave. Research over the last decade has pinned much of this on a signalling molecule called neurokinin B. The practical result is that **the comfortable band gets narrower**. A tiny rise in core temperature, one that would never have registered before, now crosses the line.
The brain responds as though you are overheating:
- Blood vessels in the skin widen to dump heat, which is the flush and the rising warmth
- You start sweating to cool down through evaporation
- Heart rate often rises for a short time
- Once the heat has gone, you are left damp and cold, sometimes shivering
A **night sweat** is the same event during sleep. It often wakes you, and even when it does not, it fragments sleep enough to leave you tired the next day. That link is worth holding onto, because broken sleep drives a lot of what people experience in perimenopause, including the brain fog that so many describe.
How Long They Last
Two different questions hide in here.
How long does one flash last? Usually one to five minutes, occasionally longer. Some people have a few a week. Others have many in a day.
How many years will this go on? This is where the common advice has been wrong for a long time. People were often told to expect six months to two years. The long running studies found something different.
The Study of Women's Health Across the Nation (SWAN) followed thousands of women through the transition. It found:
- The **median total duration** of frequent hot flashes and night sweats was about **seven years**
- Women whose flashes started **earlier in perimenopause**, while they were still having periods, tended to have them for **longer**, often more than ten years
- Women whose flashes started only after their final period tended to have them for a shorter time
- Duration also varied between ethnic groups in the study, with Black women reporting the longest duration on average
Seven years is a median. Some people have a few months of mild flashes. Others have them into their sixties. If yours are disrupting your sleep or your work, waiting them out is not the only option, and the timescale is a good reason not to.
Triggers Worth Testing
The cause is hormonal, but plenty of things push you over the edge of that narrower band on a given day. The commonly reported triggers:
- Alcohol, especially red wine and especially in the evening
- Hot drinks and caffeine
- Spicy food
- Warm rooms, heavy duvets, synthetic fabrics and tight layers
- Stress and anxiety, including a stressful meeting or an argument
- Smoking, which is also linked to more frequent and more severe flashes overall
The catch is that triggers are personal. One person gets a flash from every glass of wine, another notices nothing. Cutting out everything on a generic list is a lot of sacrifice for a result you cannot check.
A better approach is a short experiment:
1. For two to four weeks, log each flash or night sweat with the time and a rough intensity
2. Note alcohol, caffeine, spicy meals, stress and room temperature on the same days
3. Look at the pattern, then change one thing at a time and see if the log moves
A few weeks of honest records will tell you more than any list, and you will have something concrete to show at an appointment.
The Practical Things That Help
These will not switch hormonal flashes off, but they change how much each one costs you.
At night:
- Keep the bedroom cool. Around 16 to 19°C (60 to 67°F) is the range usually recommended for sleep, and cooler is often better during the transition
- Use layers of bedding you can throw off, rather than one heavy duvet
- Choose breathable cotton, linen or moisture wicking sleepwear
- Keep a glass of cold water and a spare pillowcase or top next to the bed, so a sweat does not turn into a full wake up
- Move alcohol earlier in the evening or drop it on nights that matter
During the day:
- Dress in layers you can remove quickly
- Carry a small fan
- A cold drink at the start of a flash helps some people shorten it
Weight and smoking. Higher body weight and smoking are both associated with more frequent flashes. Neither is a quick fix, but both are worth knowing about.
What the Evidence Says About Treatment
This is the part many people never get told clearly.
Hormone therapy. Oestrogen, with a progestogen if you have a uterus, is the most effective treatment for hot flashes and night sweats. For most healthy people under 60 or within ten years of their final period, current guidance from the major menopause societies is that the benefits for these symptoms generally outweigh the risks. The options, the timeline and how to tell whether it is working are covered in the HRT guide.
Non hormonal prescription options. For people who cannot take hormones, for example after some breast cancers, or who prefer not to, there are options with good trial evidence:
- Fezolinetant works directly on the neurokinin B pathway described above. It was approved in the United States in 2023, and a newer drug in the same family, elinzanetant, has since followed in some countries
- Low dose SSRIs and SNRIs, such as paroxetine, venlafaxine and escitalopram, reduce flash frequency for many people, independent of any effect on mood
- Gabapentin, particularly helpful for night sweats when taken in the evening
- Oxybutynin, a bladder medicine that has also shown benefit
Cognitive behavioural therapy. CBT designed for menopause symptoms does not usually reduce the number of flashes much, but trials show it reduces how much they bother you and improves sleep. Clinical hypnosis has similar evidence. Both are recommended in the major non hormonal guidance.
What has weak or no evidence. Black cohosh, soy isoflavones, evening primrose oil, most supplements sold for menopause, and paced breathing have not performed convincingly in good trials. Some people feel better on them, and a placebo response for hot flashes is known to be large, which is exactly why trials are needed to separate real effects from hope.
When It Is Not Hormonal
Hot flashes and night sweats are very common, which makes it easy to put every sweat down to hormones. Some deserve a closer look.
See a doctor promptly if sweats come with:
- Fever, chills or feeling unwell
- Unexplained weight loss
- A persistent cough or swollen glands in the neck, armpit or groin
- A racing heart, tremor or heat intolerance all day, which can point to an overactive thyroid
Also worth checking:
- Medications. Some antidepressants, diabetes medicines, steroids and others list sweating as a side effect
- Timing. Sweats that started suddenly and do not fit any other change in your cycle are more worth investigating than sweats that arrived alongside the other signs of perimenopause
Most of the time the answer really is the transition. The point is to rule out the alternatives rather than assume.
Why Tracking Makes the Appointment Better
Hot flashes are measurable in a way many perimenopause symptoms are not. You can count them. That makes a record unusually useful.
When you walk in with a few weeks of data, the conversation changes:
- "Six to eight flashes a day and night sweats four nights a week" is a clear case for treatment. "I get hot a lot" is easy to wave away
- If you start treatment, you can see whether it worked, rather than guessing from how you feel on a good week
- If a trigger is real, the log shows it
Where Alva Fits
Alva is a perimenopause tracker for iPhone built around the fact that this phase does not follow a neat monthly pattern.
It logs 40 symptoms including hot flashes, night sweats, sleep disruption, brain fog and mood, so you can see whether night sweats line up with worse days. Irregular cycles record without error states or false predictions. It keeps a full hormone therapy history, from patches and gels to cyclical regimens, with adherence over any range, so you can compare the weeks before and after a change in treatment. One tap turns three months of entries into a clinical PDF with ranked symptoms and sparklines, the kind of summary that fits into a ten minute appointment.
What it does not do:
- It does not diagnose anything. It cannot tell you whether a night sweat is hormonal or something else. That is what the doctor is for
- It does not recommend treatment. It helps you describe the pattern accurately so the person prescribing can decide
- It only knows what you log. A flash you did not record is not in the report
Alva is not a medical device. It is a better way to bring evidence to the person who is.
The Short Version
- A hot flash happens because falling oestrogen narrows the brain's comfortable temperature band, so tiny rises in core temperature trigger a full cooling response
- One flash usually lasts one to five minutes. The phase lasts a median of about seven years, and longer when flashes start early in perimenopause
- Common triggers include alcohol, hot drinks, spicy food, warm rooms and stress, but they are personal, so log first and cut second
- A cool bedroom, layered bedding and breathable sleepwear reduce how much night sweats cost you
- Hormone therapy is the most effective treatment. Fezolinetant, low dose SSRIs and SNRIs, and gabapentin are evidence based non hormonal options. CBT helps with the burden
- Most supplements have not held up in good trials
- Sweats with fever, weight loss, swollen glands or a persistent cough need a medical check