Hi Friend
Just a quick note, all my 1-1 appointments got booked within an hour. I have therefore opened up a few more slots here
If you’re dealing with unexplained allergic reactions, random food sensitivities, flushing, gut issues, dizziness, or “mystery” inflammation, you may have wondered:
“Is this MCAS? Or is it something more serious?”
This confusion is incredibly common, even among doctors.
Today, I want to walk you through the differences in a way that feels clear and reassuring — without the overwhelm.
What Actually Is MCAS?
Mast Cell Activation Syndrome (MCAS) is when your mast cells — the immune cells involved in allergic reactions — become oversensitive. They aren’t increased in number, but they release chemicals (like histamine) too easily and in response to triggers that shouldn’t normally cause a reaction.
People often describe it as:
“My body reacts to everything.”
“Different symptoms on different days.”
“I never know what will set me off.”
MCAS commonly overlaps with conditions like fibromyalgia, ME/CFS, POTS, EDS, long COVID, and trauma-related physiology.
It’s a pattern of reactivity, not a structural disease.
🧬 What Is Mastocytosis?
Mastocytosis is very different — and much rarer.
Instead of oversensitive mast cells, mastocytosis involves too many mast cells being produced. These abnormal cells can accumulate in the skin, bone marrow, or other organs.
It’s more of a cellular growth disorder than a reactive syndrome.
People with mastocytosis often have:
more constant symptoms
particular skin lesions (small brown spots that react when rubbed)
higher baseline tryptase levels
sometimes organ involvement
This condition usually requires specialist care.
⭐ The Easiest Way to Tell Them Apart
Here are the simplest, most reliable clues — explained in plain English.
1. Do your symptoms go up and down?
MCAS tends to fluctuate.
Good days and bad days.
Flares triggered by stress, food, heat, hormones, infections, exercise, emotions.
Mastocytosis tends to stay more steady and predictable.
2. Do you react to lots of different things?
MCAS is known for “wide trigger sensitivity”: food, chemicals, smells, stress, weather changes.
Mastocytosis usually has more specific triggers.
3. Do you have brown skin patches?
Mastocytosis often causes small brown lesions (sometimes called urticaria pigmentosa).
If these are present, further investigation is important.
If they’re not present, MCAS becomes far more likely.
4. What is your tryptase level like?
MCAS often shows a normal or slightly raised tryptase.
Mastocytosis usually shows a clearly elevated tryptase, often above 20.
5. Do antihistamines or calming strategies help?
People with MCAS often improve noticeably with antihistamines, mast cell stabilisers, low-histamine diets, or nervous system work.
In mastocytosis, these improvements can be more limited.
🔬 Do You Need Tests?
For MCAS, testing can support the diagnosis, but it isn’t always reliable.
Many people with clear MCAS have normal test results because timing and sample handling matter.
MCAS is primarily diagnosed by:
Typical symptoms
Improvement with mast-cell–directed treatments
Evidence of elevated mediators (if captured at the right time)
For mastocytosis, tests are more decisive:
persistently high tryptase
distinctive skin findings
genetic testing (KIT mutation)
sometimes a bone marrow biopsy
Most people don’t need invasive testing unless red flags are present.
🌈 The Reassuring Part
Whichever condition you have, support is possible.
For MCAS especially, people often see meaningful improvement through:
reducing overall stress load
calming the nervous system
improving sleep and pacing
gentle diet modifications
addressing trauma physiology
antihistamines or natural stabilisers
slow, steady tolerance-building
reducing inflammation
creating safety in the body
MCAS is deeply connected to the body's perception of threat — and the more we help your system feel safe, the more those mast cells calm down.
You are not “too sensitive.” Your body is trying to protect you — it’s just overfiring.
In Summary
MCAS is about overly reactive mast cells.
Mastocytosis is about too many mast cells.
MCAS is common, fluctuating, multi-system, and deeply tied to the nervous system.
Mastocytosis is rare, structural, and usually more consistent.
Most people experiencing unpredictable flares, food reactions, dizziness, gut issues, migraines, or “mystery inflammation” are dealing with MCAS, not mastocytosis.
And with the right support, things can improve — often dramatically.
Tomorrow we will discuss what you can try yourself to help with histamine issues,
Stay Well
