7 posts tagged with "Heat"

In some people with multiple sclerosis, becoming warm temporarily worsens existing symptoms. This is often called Uhthoff's phenomenon. Cooling and rest may help symptoms settle, but new, unusually severe or persistent changes need medical advice rather than an automatic assumption that heat is responsible.

MS heat intolerance can complicate ordinary tasks: a commute, a hot shower, a queue outdoors or activity in a warm room. Planning around those exposures can make the day more manageable. It does not require avoiding every activity or treating the outdoor temperature as a complete measure of your condition.

Heat intolerance means feeling unusually overheated when the surrounding temperature rises. Medicines, hormonal changes, and health conditions can contribute, so persistent or unexplained symptoms deserve a medical review. A forecast helps you prepare for exposure; it cannot tell you why heat has become difficult to tolerate.

If you find yourself saying “I cannot tolerate heat anymore,” start with the change you noticed. Does a short walk now feel overwhelming? Are episodes happening in a comfortably cooled room? Did symptoms begin after a new medicine? Those details make a better starting point than assuming every episode is caused by summer weather.

The honest answer is that climate change is very likely making conditions harder for weather-sensitive people, but not primarily through the mechanism most people assume. There is no good evidence that average barometric pressure is changing in a way that matters, and the research on whether storms are becoming more frequent is genuinely mixed. What is well documented is that the supporting conditions have shifted measurably: pollen seasons across North America have lengthened by around twenty days since 1990, wildfire smoke now routinely reaches regions that never experienced it, heat waves are longer and more intense, tropical cyclones are intensifying more rapidly when they do form, and the seasonal windows during which disruptive weather is possible have widened at both ends. For someone whose attacks track weather, the practical effect is fewer genuinely quiet months in the year.

This is a subject where overclaiming is common in both directions, so it is worth being precise about which parts are settled.

An urban heat island is the temperature difference between a built-up area and the rural land around it, typically one to three degrees Celsius as a daily average but frequently seven degrees or more on calm clear nights. The mechanism is straightforward: cities replace vegetation with materials that absorb and store solar energy, remove the evaporative cooling that plants provide, trap heat in street canyons that radiate poorly to the sky, and add waste heat from vehicles, buildings and air conditioning. For headache and migraine the significant part is not the hot afternoon, which is only modestly warmer than the surrounding countryside, but the hot night, when the difference is at maximum and sleep is what suffers. Poor sleep is among the best-evidenced migraine triggers there is, and the urban heat island systematically attacks it.

The effect is also strikingly uneven within a single city, which turns out to matter more than the city-wide average.

The North American monsoon is a seasonal wind shift that brings moisture from the Gulf of California and the eastern Pacific into Arizona, New Mexico and adjacent states from roughly late June through September. It transforms a region that spends three quarters of the year with an almost motionless barometer into one that produces some of the fastest short-term pressure changes anywhere — not from large storm systems, but from outflow boundaries racing off collapsing thunderstorms, which can jump the reading three to six hPa in under fifteen minutes. For weather-sensitive people in the Southwest, the practical consequence is that the symptom year is sharply divided, and almost everything worth tracking happens in about ten weeks.

Understanding the mechanism explains both why the rest of the year feels so stable and why the monsoon feels so unlike it.

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.

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.