Does low barometric pressure cause migraines?

It's associated, not strictly causal. Multiple cohort studies link 24-hour pressure drops of more than 5 hPa to higher migraine probability, but only in roughly 20–30 percent of people who track it. The effect is real but modest, and most attacks happen on days with no pressure change.

How big a pressure drop matters?

Published thresholds cluster around a 5 hPa drop over 24 hours. Hermly's rule engine uses the same 5 hPa threshold for the same reason — smaller fluctuations are within day-to-day weather noise and don't reliably correlate with attacks.

Can I prevent a pressure-triggered migraine?

Not directly — you cannot change the weather. What you can do is plan: hydrate earlier, prioritise sleep the night before a known pressure drop, and have your acute medication accessible. Hermly surfaces upcoming pressure drops so the planning step is yours, not the app's.

Do weather apps replace a migraine forecast app?

Weather apps tell you about the weather. A migraine app combines pressure with your sleep, cycle, HRV, and attack history to estimate today's personal risk — which can be high or low even on identical-weather days.

Barometric pressure migraine: what research shows

Creator: Hermly
Published: 2026-05-16T00:00:00.000Z

Barometric pressure is the air pressure measured at the ground — the same number a weather app shows next to “millibars” or “hPa”. When a front moves through, that number drops. Among the dozens of suspected migraine triggers, pressure is one of the very few that has held up across peer-reviewed cohort studies (Katsarava et al., Current Pain and Headache Reports, 2024). It isn’t universal — perhaps a quarter of self-reporting migraine patients show a robust association — but where it exists, it’s strong enough to be worth knowing about.

This page covers what the research actually supports, the specific threshold Hermly uses, and how pressure data flows into your iPhone’s risk forecast without ever leaving the device.

What “barometric pressure migraine” actually means

A barometric (also “atmospheric”) pressure migraine isn’t a separate diagnosis in ICHD-3 — it’s a colloquial label for migraine attacks that cluster around weather changes in a particular individual. The plausible mechanisms are still debated and likely multifactorial:

Sinus + middle-ear pressure differential as outside pressure drops, which can mechanically irritate trigeminal nerve endings.
Vasodilation in response to falling atmospheric pressure, altering cerebral blood flow.
Indirect effects — pressure drops correlate with weather fronts that also bring temperature swings, humidity changes, and shifts in ozone and pollen.

The honest answer is no single mechanism is fully established. What is established is the statistical pattern: in cohorts that track both daily attacks and local weather, pressure-drop days are modestly over-represented among attack days.

The threshold that matters: about 5 hPa in 24 hours

The published research converges on a roughly 5 hPa (≈ 0.15 inHg) drop over 24 hours as the working “event” threshold. Smaller drops are inside the noise floor of normal day-to-day variation — they don’t correlate. Bigger drops (10–15 hPa, the kind that come with strong fronts or storms) show progressively stronger associations.

Hermly uses the same 5 hPa threshold inside its rule engine: a 24h drop greater than that magnitude contributes a “Pressure” factor to today’s risk score, with the magnitude saturating at 15 hPa. The saturation matters — beyond a certain drop, the signal stops getting stronger, and we don’t want a single weather front to crowd out sleep, cycle, and HRV.

Why a pressure trigger isn’t a destiny

Two things to keep in mind:

Most attack days do not have a pressure drop. Across published cohorts (Houle 2017; HAPRED-II 2026), the largest single predictor is the user’s own recent attack pattern and self-reported stress, not weather. Pressure adds a few percentage points of AUC on top.
Individual variation is large. A handful of patients show near-deterministic pressure reactivity; many show none. The HAPRED research line found that adding weather features only meaningfully helps the subset where the within-person correlation is real.

In practice this means: if you’ve noticed personally that storms trigger you, the data probably backs you up. If you’ve noticed no pattern, you’re not failing to spot something — you may simply be one of the people for whom pressure isn’t the dominant signal.

How Hermly handles pressure on your iPhone

Hermly reads local barometric pressure from WeatherKit on your iPhone, keyed to your CoreLocation fix. Three derived features go into the model:

24-hour pressure change — the signed delta. Negative = drop.
Pressure drop event — boolean, true when the magnitude exceeds the 5 hPa threshold.
Local pressure z-score — today’s pressure relative to a 12-month history for your location. This is what lets the model distinguish “low pressure” in Denver (~840 hPa baseline) from “low pressure” in Miami (~1015 hPa).

These three numbers feed the same model that reads your sleep, cycle, HRV, and attack history. No raw pressure samples ever cross the device boundary — see our methodology page for the full data flow.

What this page is not

This isn’t medical advice, and it isn’t a treatment plan. If pressure-linked attacks are disrupting your life, the conversation to have is with a neurologist or headache specialist — they have preventive medication options (CGRP antagonists, beta blockers, topiramate) that Hermly cannot prescribe, recommend, or assess.

What Hermly does is make the data legible: today’s pressure trend, your historical correlation with it, and a calibrated risk number that gives you a head start.

Not medical advice. Hermly is a wellness app, not FDA-cleared for diagnosis or treatment. This page is informational and should not replace conversation with your doctor. If you're experiencing a sudden, severe, or unusual headache, contact a medical professional or emergency services.