Thunder, Lightning, and Sferics: Electromagnetic Weather Effects

The best evidence on lightning and headache comes from a 2013 University of Cincinnati study that tracked 90 people with migraine in Ohio and Missouri and found that headache risk rose roughly 30 percent, and new-onset headache roughly 24 percent, on days with lightning within 40 kilometres. The effect survived statistical adjustment for barometric pressure and for the general presence of a storm, which is what made it notable. But the study could not identify a mechanism, and the leading candidate — electromagnetic radiation from lightning strokes, known as sferics — remains a hypothesis rather than a demonstrated cause. Thunderstorms deliver pressure swings, humidity jumps, ozone, pollen rupture, wind, noise, disrupted sleep and light flashes all in the same package, and disentangling an electromagnetic effect from that pile is genuinely difficult.

The honest position is that something about lightning days looks real and nobody has shown what it is.

What sferics actually are

A lightning stroke is a current pulse of tens of thousands of amperes rising in microseconds. Any accelerating charge radiates electromagnetic energy, and a stroke that abrupt radiates across an enormous span of frequencies, with most of the energy in the very low frequency and extremely low frequency bands — roughly 3 hertz to 30 kilohertz.

That radiation is called an atmospheric, or sferic for short. Sferics have a physical property that makes them unusual: at those wavelengths the space between the Earth's surface and the ionosphere acts as a waveguide, so the signal propagates for thousands of kilometres with very little loss. This is how global lightning detection networks work — a handful of receivers can locate strokes across an entire hemisphere by timing arrivals.

It is also the basis of Schumann resonances, standing electromagnetic waves in that same Earth-ionosphere cavity with a fundamental near 7.8 hertz, continuously excited by the roughly forty to fifty lightning strokes occurring somewhere on Earth every second.

The numerical coincidence between 7.8 hertz and the human alpha rhythm in EEG has generated an enormous amount of speculation, much of it untethered from physics. It is worth being clear about scale: Schumann resonance field strengths are on the order of picotesla, while the Earth's static magnetic field is around 50 microtesla — roughly seven orders of magnitude larger — and ordinary household wiring produces fields far stronger than either. Any biological mechanism would have to explain how a system that ignores much larger ambient fields responds to a much smaller one. That is not impossible, but it is a high bar and it has not been cleared.

What the Cincinnati study did

The 2013 study, published in Cephalalgia by Martin and colleagues, is the most-cited work on this question and deserves a careful reading.

Design. Ninety participants with physician-diagnosed migraine kept daily headache diaries for three to six months. Participants lived in two regions, Ohio and Missouri. Lightning data came from the National Lightning Detection Network, which records stroke location, time, polarity and peak current.

Exposure definition. Lightning was counted when strokes occurred within 40 kilometres of a participant's home.

Findings. Headache probability rose about 31 percent, and new-onset headache about 28 percent, on lightning days. In the adjusted models — controlling for barometric pressure changes and other meteorological variables — a roughly 19 percent increase in headache and 23 percent in migraine persisted. The authors also reported an association with stroke polarity and peak current, which is the detail that pointed them toward an electromagnetic explanation rather than a purely meteorological one.

What the authors said. They were careful. The paper explicitly described the mechanism as unknown and listed sferics, ozone generation, fungal spore release and the sheer number of correlated meteorological variables as candidates. It framed the result as a finding that warranted further study, not a settled causal claim.

Limitations worth holding onto. Ninety participants is small. Two regions with similar continental storm climates is narrow. Diary studies depend on self-report and on participants not knowing the hypothesis, which is hard to guarantee. Most importantly, lightning within 40 kilometres is an extraordinarily strong proxy for "a thunderstorm is happening near you", and a thunderstorm changes a dozen things at once. Statistical adjustment for barometric pressure removes the linear component of one of them.

As far as I know, the finding has not been convincingly replicated in a larger independent cohort in the years since.

Everything else a thunderstorm brings

This is the crux of the problem. Consider what happens in the few hours around a convective storm:

Pressure. A mesoscale high builds under the storm's cold pool, and a wake low can follow behind it. The local pressure trace can show a rapid rise of several hectopascals and an equally rapid fall within an hour — changes far faster than a frontal passage, even if the total amplitude is smaller.

Humidity and temperature. Outflow can drop temperature ten degrees in minutes while dewpoint and relative humidity jump.

Ozone. Lightning fixes atmospheric nitrogen and generates nitrogen oxides and ozone. Ground-level ozone is an established respiratory irritant, and there is some literature linking ozone exposure to headache.

Pollen fragmentation. This is a documented, well-characterised effect. Thunderstorm outflow lofts pollen grains, and the humidity change causes them to rupture into far smaller fragments that penetrate deeper into the airway. This is the mechanism behind thunderstorm asthma, most dramatically in the 2016 Melbourne event. If your headaches have an allergic component, this is a strong candidate pathway that has nothing to do with electromagnetism.

Noise and light. Thunder is a loud, unpredictable, startle-inducing stimulus. Lightning is an abrupt high-contrast flash. Both hit people with migraine where they are already sensitive — phonophobia and photophobia are core migraine features.

Sleep. Night storms wake people. Disrupted sleep is one of the most reliably established migraine triggers there is.

Anticipation. People who believe storms trigger their headaches are more anxious when a storm is forecast, and anxiety itself is a trigger. This is not a dismissal — it is a real causal pathway that any diary study will capture.

Any of these could produce the Cincinnati result without a single photon of very low frequency radiation doing anything to a human nervous system.

Is there a plausible electromagnetic mechanism at all?

To be fair to the hypothesis, there is relevant biology, just not conclusive biology.

Magnetoreception exists in other animals. Birds, turtles and some insects detect magnetic fields, probably through cryptochrome proteins in the retina forming radical pairs whose recombination rates are magnetically sensitive. Humans have cryptochromes. Whether we have a functioning magnetoreceptive system is disputed; one study reported EEG changes in humans in response to rotating magnetic fields, which is intriguing and not widely replicated.

Transcranial magnetic stimulation works. Single-pulse TMS is an approved acute migraine treatment. This proves magnetic fields can influence cortical excitability — but TMS uses fields on the order of one tesla, which is roughly twelve orders of magnitude above sferic field strengths. It establishes that the direction is possible, not that the magnitude is.

Cortical spreading depression is the target. Migraine aura corresponds to a slow wave of depolarisation crossing the cortex. If any weak-field effect were going to matter, modulating the threshold for that wave is the most plausible place. No one has shown this happening at the relevant field strengths.

So the mechanism is not absurd. It is unsupported.

What to actually do with this

The practical advice does not really depend on which mechanism turns out to be right, which is convenient.

Treat approaching thunderstorms as a risk window. Whether it is the sferics, the ozone, the pollen fragments, the pressure swing or the noise, the storm is the observable. You do not need to know why to plan around it.

Watch the pressure trace, not just the radar. Convective pressure changes are fast and easy to miss on a daily summary. An hourly barometric pressure forecast for a storm-prone location shows the mesohigh rise and wake low far better than a once-a-day figure.

Log the specifics. If you record whether there was thunder, whether it was nearby, whether you were woken, and whether the pollen count was high, you can start to separate the candidates in your own data. Nobody else's study can do that for you.

Check the allergy pathway. If your storm headaches come with sneezing, congestion or wheeze, the pollen fragmentation route is far more likely than anything electromagnetic, and it is treatable.

Be sceptical of products. Devices sold to shield you from sferics or to generate a corrective Schumann resonance have no demonstrated effect, and the underlying claim is a hypothesis that its own originating study declined to assert.

FAQ

Does lightning cause migraines? One reasonably designed study found an association that survived adjustment for barometric pressure. That is a real finding, but association is not causation, the sample was small, and replication is lacking. The safer statement is that thunderstorm days carry elevated headache risk for some people, with the responsible factor unidentified.

How far away does lightning have to be to matter? The Cincinnati study used a 40 kilometre radius and found the effect within it. Sferics propagate thousands of kilometres, so if the electromagnetic hypothesis were correct you would expect distant storms to count too — and the fact that the effect appears tied to nearby lightning is arguably an argument against the sferic mechanism and in favour of the local meteorological one.

What are Schumann resonances and do they affect health? Standing electromagnetic waves in the cavity between the Earth's surface and the ionosphere, excited by global lightning, with a fundamental near 7.8 hertz. There is no reliable evidence of health effects. The field strengths involved are minute compared to ambient fields we demonstrably ignore.

Could it just be the pressure change? Partly, probably. The Cincinnati authors adjusted for barometric pressure, but adjustment handles the variable as measured and modelled, and convective pressure structure is complex, short-lived and poorly captured by hourly station data. Residual confounding is a real possibility.

Is thunderstorm asthma related? It is a well-established and separate phenomenon, driven by pollen grains rupturing into respirable fragments in storm outflow. If you have both allergic disease and headaches, it is a plausible shared pathway and worth discussing with a clinician.

Should I take acute medication when a storm is forecast? That is a decision for you and your clinician, and it depends on your attack frequency, your medication and your overtreatment risk. For people with a clear, repeatable storm pattern, pre-emptive strategies are sometimes appropriate — but the threshold for medication overuse headache is low, and a forecast is not the same as an attack.

Does the polarity of a lightning stroke really matter? The Cincinnati study reported an association with polarity and peak current. Positive strokes are less common but carry much higher peak currents and radiate more strongly. This is the part of the finding that most suggests an electromagnetic route — and also the part most likely to be a chance result in a small sample.

The short version

Lightning days appear to carry somewhat higher headache risk. The sferic hypothesis is interesting, has a real physical basis for long-distance propagation, and has never been shown to operate in humans at the field strengths involved. Meanwhile a thunderstorm delivers a rapid pressure oscillation, an ozone pulse, ruptured pollen, loud noise, bright flashes and interrupted sleep, any of which would explain the finding without new physics.

Plan around the storm rather than the mechanism, and use a migraine tracker app alongside a barometric pressure forecast to find out which part of the package is yours.