The Hell of Humidity
Discussions of the effects of warmer weather are common in publications geared towards MS. However, one aspect of this weather that I feel doesn’t get its due is the effects of increased humidity. As we have been going through a period of intense humidity where I live in the mid-Atlantic United States, this seems like as good a time as any to talk about it. Increased humidity can be extremely devastating to someone with MS, even when the ambient temperature is fairly mild. Increased humidity alone is enough to raise our body temperatures and bring about a rapid worsening of symptoms.
MS and increased temps
As mentioned many times in previous articles, an increase in body temperature for someone with MS can bring about a temporary worsening of symptoms. Increased temperature affects the speed at which signals on our damaged nerves travel. So the more myelin you’ve had damaged or eaten away by your immune system, the worse you will be in the heat. Areas that may be damaged, but not enough to be a problem, suddenly become problem areas when the temperature rises. When my body temp increases, I have trouble walking, I slur my speech, my right arm becomes numb, and my vision blurs. I start revisiting the symptoms of the many exacerbations I’ve had over the years.
Humidity and evaporative cooling
So what makes humidity such a problem? Most people know that the more humid it is, the warmer they feel. We even have the “Heat Index”, which is a chart that takes the temperature and relative humidity and figures out what the temperature actually feels like to us. So higher humidity makes us feel warmer, but why? Without trying to get too sciencey, it’s because it affects our body’s ability to cool itself. One of the key ways the human body helps regulate its temperature is through sweating. It does this through the process of evaporative cooling (you may see cooling towels and other products that advertise themselves as working through evaporative cooling, our bodies come with this handy feature built in). In a very basic explanation, evaporative cooling works like this: liquid changes into a gas (vapor) by shedding molecules into the air, those molecules draw heat from the hotter air, cooling them down as the liquid and air find an equilibrium; this also cools the surface where the liquid was, because the hotter molecules of that liquid are more likely to escape into the air and become vapor first. When humans sweat, our bodies are taking advantage of this process. A liquid (sweat) comes out onto our skin, evaporates and that process of the sweat becoming vapor cools us down.
When sweating no longer cools us down
Here is where humidity becomes a problem. Humidity is essentially the amount of water vapor in the air: the higher the humidity, the more of that water vapor is present. The more water vapor already in the air, the less it can accept through evaporation. This means that we can sweat and sweat but because there is already so much moisture in the air, it can’t evaporate and so the process of sweating no longer cools us down. So the higher the humidity, the worse our body is at being able to cool itself and regulate its own temperature.
It can be hard to battle humidity, so it’s important to be aware of it. Recognize and inform your friends and family that it’s not only warm temperatures that you need to be wary of, but high humidity as well. If you experience a temporary worsening of symptoms, try not to panic, but understand that you need to cool off. Ice packs and a cold shower are often very helpful. However take note, there are a lot of cooling devices that work through ”evaporative cooling” (many are towels you soak and then put around your neck). Those products won’t be very effective when the humidity is high, for all the same reasons that your sweating isn’t effective. It’s not that the products are defective, it’s that they don’t do a great job explaining when they will and won’t work.
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