MCAS Is Not Always Visible on the Skin: Why It Goes Unrecognized
When most people hear the term mast cell activation syndrome (MCAS), they immediately think of skin symptoms like hives, flushing, or itching. While these symptoms can be part of the picture, they’re not always present—and focusing solely on what’s visible can lead to misdiagnosis, delayed treatment, and invalidated experiences.
What Is MCAS?
MCAS is a condition in which mast cells—part of the immune system—release excessive or inappropriate amounts of chemicals like histamine, prostaglandins, and cytokines. This leads to a wide range of symptoms affecting multiple systems in the body.
To meet diagnostic criteria, symptoms must involve at least two different organ systems—but those symptoms may not always be visible externally.
The Common Misconception: MCAS = Skin Issues
Many healthcare providers and patients alike associate MCAS with skin-related symptoms, such as:
Hives
Flushing
Itching
Rashes
Dermatographia
While these symptoms are common, they are not required for an MCAS diagnosis. Some people with MCAS have no skin symptoms at all.
MCAS Is a Multi-Systemic Condition
Mast cells are found throughout the body, not just the skin. That’s why MCAS symptoms can show up in many different organ systems, including:
Gastrointestinal, such as nausea, vomiting, diarrhea, abdominal pain, bloating, or food intolerances
Neurological, such as brain fog, headache or migraine, dizziness, or imbalance
Cardiovascular, such as rapid heart rate (tachycardia), low blood pressure, or blood pressure swings, lightheadedness, or fainting
Respiratory, such as shortness of breath, nasal congestion, or asthma-like symptoms
Musculoskeletal, such as widespread pain, joint or muscle aches, or fatigue
Some people also experience anaphylaxis-like episodes without a clear allergic trigger—another sign that mast cells are involved.
Why Skin-Only Narratives Can Be Harmful
When skin symptoms are used as the default or only image of MCAS, many patients get overlooked. Those without visible symptoms may be told their illness is “anxiety,” “IBS” (irritable bowel syndrome), or “in their head.” This delays diagnosis and treatment, and can lead to emotional distress and isolation.
Validation starts with education. Healthcare providers, caregivers, and the public need to understand that MCAS can be an invisible illness—and that skin involvement is just one part of a much bigger picture.
The Importance of Early Recognition
The sooner MCAS is recognized, the sooner patients can start taking steps toward stability. When MCAS is viewed through a multi-systemic lens, it becomes much easier to connect the dots—and offer patients real support.
Just because you can’t see it doesn’t mean it’s not real. MCAS can silently affect nearly every system in the body. Flushing and hives are only part of the story—and sometimes, they’re not part of it at all.
By broadening awareness of MCAS and recognizing its invisible nature, we can help more people get the validation, care, and treatment they need.
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Disclaimer: This blog post is for informational purposes only and shall not be construed as behavioral health or medical advice. It is not intended or implied to supplement or replace treatment, advice, and/or diagnosis from your own qualified healthcare provider.