Detailed definition
Hot flashes, formally vasomotor symptoms (VMS), are episodes of sudden cutaneous vasodilation, sweating, and a sensation of intense heat that typically last 1–5 minutes. The mechanism involves estrogen-sensitive thermoregulatory neurons in the hypothalamic preoptic area. Estrogen withdrawal narrows the "thermoneutral zone" — the temperature range over which the body can dissipate heat through normal mechanisms — so smaller temperature increases trigger a full vasodilation-and-sweat response. The neurokinin B / KNDy (kisspeptin/neurokinin B/dynorphin) neuron system in the arcuate nucleus has been identified as a key downstream pathway, which is the basis for fezolinetant's mechanism. VMS prevalence in the US is roughly 75–80% of women across the menopause transition. Mean duration of moderate-to-severe VMS is 7.4 years (Avis et al., SWAN study), with women who develop symptoms in early perimenopause experiencing the longest duration. HRT reduces VMS frequency by 75–90% and severity proportionately. Non-hormonal options include fezolinetant, low-dose paroxetine, SNRIs (venlafaxine), gabapentin, oxybutynin, and clonidine.
Why it matters in menopause
Hot flashes are the most common reason women seek menopause care and the symptom HRT treats most reliably and quickly — typically within 2–4 weeks of starting estradiol. For women with absolute contraindications to estrogen, fezolinetant is a meaningful option that targets the underlying neural pathway directly without raising estrogen.