13 posts tagged with "Altitude"

Outdoor glare headache is caused by luminance contrast, not by total brightness, and that distinction decides what actually helps. A uniformly bright overcast sky and a low winter sun glinting off wet tarmac can measure similar overall light levels while producing completely different amounts of discomfort, because glare is what happens when one part of your visual field is dramatically brighter than the part your eye is adapted to. Snow, water, wet roads and glass are the main culprits, and all four are worst when the sun sits low. The practical responses are polarisation for reflected glare, a brimmed hat for sky glare, tinted lenses in the FL-41 range for the specific wavelengths that drive migraine photophobia, and — importantly — avoiding dark sunglasses indoors, which makes light sensitivity worse over time rather than better.

Snow blindness is a separate injury with a separate mechanism, and it is worth understanding on its own terms.

The UV index is a forecast of ultraviolet radiation intensity, and ultraviolet light is almost certainly not what triggers your migraine. Photophobia in migraine is driven by visible light, with the strongest response in the blue range around 480 nanometres, through a retinal pathway that connects intrinsically photosensitive ganglion cells to pain-processing regions in the thalamus. Ultraviolet radiation sits below 400 nanometres, outside the visible range, and is largely absorbed by the cornea and lens before it reaches the retina at all. The UV index is still a useful proxy, because the conditions that produce a high UV index — clear skies, high sun angle, altitude, reflective surfaces — are the same conditions that produce intense visible brightness and glare. But treating it as a direct trigger leads to the wrong protective choices, most obviously wearing sunglasses that block UV while doing little about the brightness that is actually the problem.

Getting this distinction right changes what you buy and when you plan around it.

Your weather app almost certainly shows sea level pressure, not the actual pressure where you are standing. The two differ by roughly 1 hectopascal for every 8 metres of elevation, which means a barometer in Denver genuinely reads around 840 hPa while the app reports something close to 1015. The adjustment exists so that a weather map can show where the highs and lows actually are, rather than a picture of the terrain. For anyone tracking symptoms against pressure, the adjustment is harmless and arguably helpful, because what the body responds to is change over time, and the adjustment is a near-constant offset that does not affect change.

The confusion this causes is common enough that it is worth walking through properly, especially if you own a home barometer or a weather station that reports something different from your phone.

Altitude acclimatization is governed almost entirely by one variable: how fast you ascend. Above roughly 3,000 metres, increase your sleeping altitude by no more than 300 to 500 metres per night, and take a full rest day every third day or every 1,000 metres gained. Climb high and sleep low if the terrain allows. Everything else — hydration, food, avoiding alcohol, and in some cases acetazolamide — helps at the margins, but none of it substitutes for going up slowly.

The reason this advice is so specific is that acclimatization is a set of physiological changes that take a fixed amount of time. You cannot will them to happen faster.

Several large population studies have found that people living above roughly 2,000 metres report migraine more often than people at sea level, with the effect strengthening above 3,000 metres. The most-cited work, a Nepalese population survey, found migraine prevalence rising with residential altitude in a stepwise fashion, and studies in Peru, Turkey and Colorado point the same way. The effect is modest — this is a shift in the odds, not a transformation — and it appears to be driven by sustained mild hypoxia rather than by pressure as such.

That distinction matters, because it explains why living high feels different from sitting through a storm.

A car can take you from valley floor to 3,000 metres in under an hour. That is a pressure drop of roughly 150 to 200 hectopascals in forty minutes — about ten times faster than the sharpest weather system you will ever sit through. The headache that follows is usually a combination of mild hypoxia, sinus and middle-ear pressure that has not equalised, and in migraine-prone people a genuine attack triggered by the rate of change. Slowing the ascent where you can, stopping at the top before descending, and actively equalising your ears on the way up are the three things that make the most difference.

The key point is that speed of change matters independently of how high you actually go.

No study has followed migraine sufferers who relocated from high to low elevation, so there is no direct evidence either way. The population research linking altitude to migraine prevalence is cross-sectional — it compares different people in different places, not the same person before and after a move. Anecdotally, some people improve substantially and others notice nothing. Given that moving house is expensive and irreversible, the sensible approach is to test it with an extended stay and a symptom log before making any decision.

The gap between what the population data shows and what it can tell an individual is the whole story here.

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.

For people who are sensitive to weather and pressure changes, flying can feel like a stress test. A storm front might lower the barometric pressure around you by a small amount over many hours; a flight compresses a much larger pressure change into the few minutes of climb and descent. That speed is exactly what tends to provoke symptoms — from ear pain and sinus pressure to a full-blown airplane headache.

This article explains what happens to cabin pressure during a flight, why it affects pressure-sensitive people and migraine sufferers in particular, and the practical steps that make air travel more comfortable.

Some people assume altitude should help.

If barometric pressure is lower in the mountains all the time, maybe the body gets used to it and weather-triggered migraines happen less often.

That idea sounds reasonable, but the real answer is more complicated.

Barometric pressure decreases as altitude increases. That is a normal physics rule, not a sign that the weather is automatically worse in a higher-elevation place.

This matters because many people compare pressure readings online without realizing that elevation changes the baseline.