MCAS and Allergies

MCAS is one of the conditions some people experience alongside Long Covid. It can cause a wide range of symptoms across the body, including but not limited to allergy-type reactions.

What are mast cells and MCAS?

Mast cells are immune cells found throughout the body. They help the body respond to threats by releasing chemical signals (including histamine and many others).

In mast cell activation disorders (MCADs), mast cells can become overactive and release these chemicals too easily or too often.

What it can feel like

MCAS can look very different from person to person. Symptoms may affect more than one part of the body and can fluctuate. Not everyone experiences all symptoms, and symptoms can vary in severity.

  • flushing, itching, hives, rashes

    • fast heart rate or palpitations

    • dizziness, lightheadedness, feeling faint

  • nausea, diarrhoea, bloating, reflux, abdominal pain

    • chest tightness, breathlessness

    • throat irritation, hoarseness, congestion

    • headaches or migraine

    • fatigue, feeling shaky or unwell

    • brain fog or feeling overstimulated

  • anxiety-like symptoms, irritability, sleep disruption

Triggers people notice

Triggers can vary widely. Some people notice flares after:

  • certain foods or alcohol

  • heat, cold, or sudden temperature changes

  • stress

  • exertion

  • fragrances, cleaning products, smoke, pollen

  • infections, poor sleep, or hormonal changes

A helpful first step: notice patterns

  • which symptoms you get and how quickly they start

  • what happened beforehand (food, environment, stress, exertion)

  • how long symptoms last and what helps them settle

This can support more informed conversations with a healthcare professional.

RESOURCES

Long Covid Scientific Consultancy, Mast Cell Action, The Mast Cell Disease Society, Allergy UK

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