The clearest separators are these. Altitude headache is usually on both sides of the head, dull and pressing, arrives six to twelve hours after gaining altitude, is worse at night and on waking, and improves when you go down. Migraine is usually one-sided, throbbing, comes with light and sound sensitivity and sometimes aura, follows your own established pattern, and responds to your usual acute medication. Altitude headache responds to descent and to oxygen; migraine largely does not. When the two are genuinely indistinguishable, treat it as altitude sickness — because that is the diagnosis where getting it wrong is dangerous.

Altitude can also trigger a real migraine attack in someone who gets them, which means both can be true at once.

Acute mountain sickness is defined by a headache appearing within roughly six to twelve hours of arriving above about 2,500 metres, together with at least one of nausea or loss of appetite, unusual fatigue, dizziness, or difficulty sleeping. It is common — depending on the ascent rate, somewhere between a quarter and half of people arriving at 3,500 metres will get it. It is also usually self-limiting. The signs that matter most are the ones that suggest it is progressing to high altitude cerebral or pulmonary oedema: confusion, an unsteady walk, or breathlessness at rest. Those mean descend, immediately.

Knowing the difference between an uncomfortable first night and a genuine emergency is the whole point of learning the symptom list.

A pressurised airliner cabin does not hold sea-level pressure. It holds the equivalent of somewhere between about 6,000 and 8,000 feet of altitude — roughly 750 to 810 hectopascals against sea level's 1,013. Regulations cap the cabin altitude at 8,000 feet under normal operations, and most older aircraft sit close to that limit. The consequence is that on a long flight you spend several hours breathing air about a quarter thinner than the air on the ground, and you get there through a pressure change far faster than any weather system could produce.

Understanding cabin pressure explains most of what people notice about flying: the ear popping, the swollen ankles, the dry throat, the sudden headache on descent, and why an empty water bottle crumples when you land.

Aeroplane ear — barotrauma of the middle ear — happens when the Eustachian tube cannot admit air into the middle ear fast enough to match rising cabin pressure during descent. The eardrum is pulled inward, which causes fullness, muffled hearing and pain. Ascent rarely causes trouble because expanding air vents outward on its own; descent requires active equalising, which is why it accounts for the overwhelming majority of cases. The single most effective prevention is starting to equalise at the beginning of the descent rather than when the pain begins.

Most cases resolve within hours. A minority do not, and knowing which is which is the useful part.

A headache on a plane usually has one of four causes: sinus or ear pressure that fails to equalise, dehydration in air drier than a desert, a disrupted sleep and caffeine schedule, or hours in a bad neck position. Each has a different fix, and the most effective interventions happen before you board rather than at 35,000 feet. If you get headaches on most flights, the highest-yield changes are treating congestion in advance, equalising early and often on descent, and keeping your caffeine timing normal rather than heroic.

This is the practical companion to the physiology. If you want the mechanism, start with what actually happens at 8,000 feet or the specifics of airplane headache as a diagnosis.

Airplane headache is a distinct condition with formal diagnostic criteria in the International Classification of Headache Disorders. It is severe, almost always one-sided, concentrated around or behind one eye, tied specifically to ascent or descent, and it resolves within thirty minutes of the pressure change ending. That last feature is what separates it from a migraine, which does not politely stop when the plane lands. Descent triggers roughly three-quarters of cases, and the leading explanation is a pressure imbalance in the sinuses.

If you have had a stabbing pain behind one eye as the plane came down and wondered whether it was a migraine, the answer is probably no — and that matters for how you treat it.

A haboob is a dust wall pushed out ahead of a collapsing thunderstorm, arriving with almost no warning and dropping visibility to near zero within minutes. It brings a genuine barometric and wind signature, particulate concentrations that can exceed hazardous thresholds many times over, and — in the American Southwest and parts of central California — a documented risk of fungal infection. The health advice is unusually simple: get indoors, close everything, and if you are driving, pull completely off the road and turn your lights off.

If you live in a dust-prone region, this is one of the few weather events where the immediate physical risk outweighs any question about headaches.

A sea breeze produces a real but small pressure change — typically one to two millibars as the front passes, against the ten to thirty millibars a storm system delivers. What makes it worth knowing about is that it happens on a schedule, most afternoons in the warm season, and it arrives packaged with abrupt shifts in temperature, humidity and wind. If your worst days cluster in coastal summer afternoons, the pressure is probably the smallest part of what is hitting you.

If you live within twenty miles of a coast and your symptom log looks frustratingly noisy from May to September, this is one of the reasons.

The number most apps show you is the sustained wind speed, averaged over ten minutes. It is the least useful of the four wind fields available. Gust speed, wind direction and the timing of the onset tell you far more about whether a day will be difficult, and all three are usually available if you know where to look. Wind is also among the best-forecast variables in meteorology — reliably good three to five days out, which is considerably better than you get for rainfall timing.

If you have decided that windy days go badly for you, the next step is learning to see them coming with enough precision to act.

Wind itself is not obviously a headache trigger. What wind reliably indicates is a steep pressure gradient somewhere nearby, and what wind reliably delivers is a package of secondary effects: rapid temperature change, humidity swings, constant low-frequency noise, disturbed sleep, cold exposure on the head and neck, and airborne particles. The honest answer is that we cannot yet separate these, and that for most people it does not matter much which one it is — the day is the trigger.

If you have noticed that gusty days go badly for you and felt slightly silly saying so, the reasoning below is more solid than you might expect.

Chinook winds are the one downslope wind with reasonably good published evidence for a migraine link. A University of Calgary study following migraine patients through chinook conditions found the odds of a migraine rose on chinook days, with the strongest effect on the day before the wind arrived and on high-wind chinook days. That is a more specific finding than exists for any other named wind. It does not mean everyone in Calgary reacts, and it does not settle the mechanism — but if you live on the eastern slope of the Rockies and your bad days cluster in winter, chinooks are worth logging as their own category.

If you are trying to work out why your worst headaches in Alberta land in January rather than July, this is the place to start.

Desert winds differ from downslope winds like the foehn and chinook in one decisive way: they carry mineral dust, often in enormous quantities, and the health evidence for airborne dust is far stronger than the evidence for wind alone. Saharan dust outbreaks have been linked in published research to increased respiratory and cardiovascular hospital admissions, worsened asthma, and — with weaker but real support — increased headache and migraine reports. If you live around the Mediterranean, in North or West Africa, the Middle East, or the desert Southwest of the United States, dust episodes are the part of the picture worth acting on.

The wind is uncomfortable. The dust is the health issue.

The alpine foehn is the original weather-sickness wind. German-speaking Europe has a word for the syndrome — Föhnkrankheit — and complaints of headache, irritability, fatigue and poor sleep during foehn conditions are so embedded in Swiss, Austrian and Bavarian culture that they appear in weather forecasts and workplace conversation. The research is more equivocal than the folklore. Studies find associations with headache and mood in some populations and fail to find them in others, and the biological mechanism remains unproven. What is not in dispute is that a foehn changes temperature, humidity, wind and the pressure field simultaneously and dramatically, and that some people reliably feel it.

If you live in the Alps or their foreland and your bad days do not line up with storms, the foehn is the obvious thing to check.

The positive ion theory is the most frequently repeated and least well supported explanation in weather-health writing. The claim is that hot dry winds like the foehn, chinook and Santa Ana raise the concentration of positively charged air ions, which then alter serotonin metabolism and cause headache, irritability and fatigue. The theory dates to the mid-twentieth century, is heavily promoted by companies selling negative ion generators, and has not held up well under modern testing. A Cochrane-style systematic review of air ionisation for depression found no consistent benefit. If you are trying to understand why a foehn day feels bad, temperature, humidity, sleep disruption and particulate exposure are better-evidenced places to look.

This article exists because the theory appears everywhere, and it is worth knowing why to discount it.

Wind chill measures how fast exposed skin loses heat, not how cold the air is. That distinction matters for headache because the plausible mechanisms — cold-induced blood vessel constriction in the scalp and face, trigeminal nerve stimulation, and muscle tension from bracing against cold — all depend on the rate of skin cooling rather than on the thermometer reading. A calm day at -10°C and a windy day at -1°C can produce similar wind chill values and similar exposure. Cold is an established headache trigger for a subset of people, and the practical response is unglamorous but effective: cover your head, face and neck.

If your winter headaches start on the walk rather than indoors, this is the mechanism worth understanding.

Air temperature measures the heat of the air. Heat index estimates what that heat does to a human body once humidity is accounted for, because sweating only cools you if the sweat can evaporate. At 90°F and 40% relative humidity the heat index is about 91°F — essentially the same. At 90°F and 80% humidity it is about 113°F. The air has not changed temperature, but your ability to shed heat has collapsed, and the physiological load is closer to a 113° day. That gap is the entire point of the number.

If you track symptoms against weather, this distinction matters. Two days with identical highs can place completely different demands on your circulation, hydration and sleep. Logging the temperature alone hides that.

Keep indoor relative humidity between 40 and 50%. Below about 30%, the mucociliary system that clears your nose dries out: mucus thickens, cilia slow, the mucosa cracks and the nose responds by swelling. Above about 55 to 60%, dust mites and mould proliferate, and for anyone sensitised to either, that means allergic inflammation and congestion. The band between them is the only region where both problems are simultaneously minimised. It is narrow because the two failure modes approach from opposite directions.

Most people who feel congested indoors are on one side of that window or the other, and the fix is different depending on which.

Muggy weather makes you tired because humid air blocks your main cooling system, and your body compensates in ways that are metabolically expensive. When sweat cannot evaporate, your heart rate rises, blood is diverted to the skin, plasma volume falls, and core temperature drifts upward. That cardiovascular work happens whether or not you are exercising. Add disrupted sleep from warm nights and mild dehydration from fluid loss without cooling benefit, and the fatigue is not psychological — it is the predictable output of a body running a continuous background load it does not run on a dry day.

The subjective experience is distinctive: heavy limbs, poor concentration, a reluctance to move, and a sense that ordinary tasks cost more than they should. Nothing about that is imaginary.

Almost certainly the pressure, not the rain. Rain is a consequence of rising air in a low-pressure system, not a cause of anything physiological. The barometric fall that produces the rain typically begins 12 to 36 hours before the first drops, and that is the window in which most people who report rain headaches actually experience symptoms. If your headache reliably starts before the rain rather than during it, you have your answer — you are responding to the pressure change, and the rain is simply the most visible marker of a system that was already affecting you.

The distinction is not academic. It determines whether a forecast is useful to you and whether anything you do in advance can help.

Santa Ana winds combine four things that each independently plausibly affect headache: a rapid temperature rise, a collapse in humidity to single digits, a reversed pressure gradient with downslope compression, and a surge in airborne dust and particulates. That combination is why the winds have a long-standing reputation in Southern California as a headache trigger, and why they are difficult to study — no single variable can be isolated. The evidence for specific health effects is more mixed than the folklore suggests, but the wildfire and air quality link is well established, and the subjective reports are consistent enough across decades to be worth logging.

If you live between Santa Barbara and San Diego and your symptoms cluster in October and November, the winds are the first thing to check against your log.