Mast cells are part of your immune system and help protect your body.

They are immune cells that store important chemicals your body uses for protection—including histamine, heparin, and various enzymes. Inside each mast cell are many tiny “packets” (called granules) that safely hold these substances until they are needed.

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When the body senses a trigger — such as an allergen, infection, stress, or injury — mast cells can release these chemicals quickly. This process is called mast cell degranulation.

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The chemicals released help the body respond and heal, but sometimes too many are released or they are released too easily. When this happens, it can cause allergy-type symptoms or inflammation.

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Common symptoms may include:

• Hives or itchy skin
• Flushing or feeling suddenly warm
• Swelling
• Runny nose or breathing changes
• Abdominal pain, nausea, or diarrhoea
• Dizziness or low blood pressure in more severe cases

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In some people, mast cells are more sensitive, which means symptoms may occur more often or with smaller triggers.

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The link between CO2 and Mast Cell Degranulation

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Carbon dioxide (CO₂) is not just a waste gas — it actually helps regulate inflammation and keeps certain immune cells calm, including mast cells.

When CO₂ levels drop too low (from chronic over-breathing or hyperventilation), several things can happen:

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• Mast cells may become more reactive or unstable.

• The body becomes more prone to releasing histamine and inflammatory chemicals.

• This can increase allergy-like symptoms, airway sensitivity, flushing, or inflammation.

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In simple terms: Healthy CO₂ levels help keep mast cells stable. Low CO₂ can make mast cells more trigger-happy.

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What may be happening physiologically (simplified science):

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Research suggests a few mechanisms linking low CO₂ (hypocapnia) with mast cell activation:

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1.CO₂ helps suppress mast cell degranulation

Studies show that higher CO₂ levels can reduce mast cell histamine release by limiting calcium signalling inside the cell — and calcium influx is a key trigger for degranulation. When CO₂ levels drop, that stabilising effect may be reduced.

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2.Low CO₂ increases alkalinity (respiratory alkalosis)

Hyperventilation lowers CO₂ → raises blood pH.

Changes in pH can:

• alter ion channels

• increase nerve excitability

• influence immune cell activation

This environment may make mast cells easier to activate.

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3. Nervous system effects

Low CO₂ often accompanies:

• sympathetic nervous system activation

• stress response

• airway dryness/cooling

These factors can indirectly promote mast cell activation in individuals.

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4. Tissue oxygen and vascular effects

Low CO₂ causes blood vessels to constrict.

This can:

• reduce oxygen delivery locally

• increase tissue stress signals

• potentially promote inflammatory signalling.

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How this relates to breathing:

People with chronic overbreathing, anxiety-driven hyperventilation, dysfunctional breathing patterns or asthma or airway hypersensitivity may experience reduced CO₂,  increased airway inflammation and mast cell mediator symptoms.​

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This is one reason gentle nasal, slow, diaphragmatic breathing approaches may help stabilise symptoms by:

• supporting healthy CO₂ levels

• reducing sympathetic overdrive

• increasing vagal tone (parasympathetic regulation)

• stabilising airway and nerve sensitivity.

Think of CO₂ like a “calming brake” on the immune system.

• Normal CO₂ = mast cells stay balanced.

• Low CO₂ = brake comes off → mast cells react more easily.

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