Pressure Change Causing Anaphylaxis (MCAS)?

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This perplexes me. I’ve heard of pressure changes causing a lapse in the immune system that would make someone more sensitive to allergens, but I’ve never heard of a full-blown episode being triggered solely from pressure changes. Someone mentioned they had “Mast Cell Activation Syndrome” (MCAS), and that this was a legitimate reality for them. They said they would board a plane and the simple pressurization of the chamber would trigger it.

What is actually happening here?

In: Biology

2 Answers

Anonymous 0 Comments

Unsatisfying answer but there is likely no known explanation for why pressure changes would trigger your friend’s MCAS.

Mast cells normally play a role as activators of inflammatory responses in your body. Mast Cell Activation Syndrome is when those cells abnormally activate, causing the constellation of symptoms known as MCAS.

Unfortunately, it is challenging to diagnose MCAS as symptoms vary widely from patient to patient and can affect multiple organs. The symptoms (allergic reactions/anaphylaxis/near-anaphylaxis) are also not unique to MCAS and could be caused by other diseases.

Different types of mast cell activation disorders also have similar presentation and inconsistent definitions and diagnostic criteria, making it harder to diagnose and identify specific triggers or why they occur.

Anonymous 0 Comments

Not a satisfying answer, but the reality is that an immune response can be triggered by nearly anything. If it can affect the body at all, then it can likely trigger an immune response. And unless it’s extremely common (and often even then), our explanations will be mostly assumptions.

Here’s the context at least: The “fun” thing about the immune system is that it is based on true randomness and automated guesswork. The underlying potential triggers get seeded using a “literally every possible thing” approach, but starting with everything deactivated. And then over time the body “decides” which ones of this randomly-generated and near-infinite set of triggers to pay attention to.

In theory this allows the immune system to learn and adapt over your lifetime, identifying and destroying threats that didn’t even exist when you were born. Mostly preserving immunity to harmful things, while hopefully not making you “immune” to yourself or your normal environment. Hopefully.

Except… how does the body “decide” that something is harmful and warrants a specific response? It can’t actually _know,_ and instead has to guess based on what stuff was noticed when bad things happened. The trigger markers don’t actually correspond to anything in particular; they’re randomly designed with nearly infinite variety, so practically anything can trip a signal, and potentially things like temperature and pressure can change the thresholds for activation.

In other words, very small changes make very big differences on a person-by-person basis over time.

**So then here’s the issue:** All answers about the immune system are incomplete guesses. Every immune system is different, and each is also different over time. We can’t always just study one and understand another. We can generalize and make sweeping statements, but we’ll be wrong a significant part of the time.

And the syndrome you’re describing is one of those corner cases where it’s hard to tell how many of our assumptions are already out the window.