Histamine Intolerance vs MCAS: Understanding the Difference.
Histamine intolerance and mast cell activation syndrome – Are you feeling a little overwhelmed?
Do you believe that your symptoms are due to histamine intolerance? Or you have heard of Mast Cell Activation Syndrome (MCAS), and you just aren’t sure whether it’s that?
Which one do you have?
It can be confusing and overwhelming to learn and understand the differences between histamine intolerance and mast cell activation syndrome.
Good news, in today’s blog, I’ll go over what histamine intolerance is and what mast cell activation syndrome is and cover some key points on both.
Histamine intolerance and mast cell activation syndrome are tricky because you can often have both!
The symptoms of both can be very similar, and sometimes it can be hard to tell where the symptoms are coming from. Understanding the difference between histamine intolerance and mast cell activation can help you to manage them better.
Let’s start with histamine intolerance:
What is Histamine Intolerance?
Histamine intolerance occurs when the body doesn’t have enough of the enzymes required to break down histamine. These enzymes are known as DAO diamine oxidase (DAO) and histamine N-methyltransferase (HNMT). When these enzymes are deficient, histamine is reabsorbed into the intestines and carried through the bloodstream in its active form.
This excess histamine causes symptoms that mimic an allergic reaction, such as sinus issues, a runny nose, etc. It may also include other symptoms like headaches/migraines, acid reflux, nausea, pain, digestive issues, night-time overheating, insomnia, skin issues, PMS and many more. To read more about histamine intolerance, click here.
What is Mast Cell Activation Syndrome?
Mast Cell Activation Syndrome (MCAS) is when your mast cells become overly sensitive. They overreact to triggers.
To understand Mast Cell Activation Syndrome, it can also help to understand a little more about what mast cells are and their role in the body.
Mast cells are a type of white blood cell that is found in connective tissues in the body. Including under the skin, in blood vessels and lymph, in the nerves, sinus, bladder and in the lungs and intestines.
Mast cells play an important role in the immune system. They help to protect us from infection and respond to certain bacteria and parasites. Mast cells are allergy cells responsible for the immediate allergic reaction. They cause allergy symptoms when they release products called mediators. The mediators consist of inflammatory cytokines and you guessed it, histamine! These mediators are stored inside the mast cells. When these mediators are triggered, it’s called activation. The release of these mediators is called degranulation.
A mushroom or a mast cell?
As an analogy for a mast cell, think about those mushrooms that release puffs of spores. the spores (mediators) stay inside until something triggers the mushroom to release them. When released these spores float on the wind until they find somewhere to settle and grow. In the body, they flow through the bloodstream until they find a receptor to connect to – which then causes symptoms.
When someone has mast cell activation syndrome, this normal process is on hyperdrive. The mast cells are more sensitive and reactive, more degranulation occurs more frequently, and so the symptoms arise. In some people, more mast cells are present than normal. For example, in IBS, higher numbers of mast cells are frequently found in the digestive tract. When this is exceptionally high or if the mast cells are not normally shaped, then Mastocytosis may be considered.
Also, many people can have a small amount of mast cell activation, but not enough to be considered full-blown MCAS. This is due to the strict diagnostic criteria for MCAS and the different criteria used in different countries and with different doctors. If you have a small number of symptoms, it is more likely to be some more minor mast cell activation (think one or two mushrooms puffing out spores) rather than MCAS (think 100 football fields full of mushrooms puffing out spores).
Histamine symptoms vs MCAS symptoms
Many symptoms of histamine intolerance and mast cell activation overlap.
Histamine Symptoms:
Migraines/headaches
Sinus issues
Hives
Digestive issues – heartburn/reflux, IBS, SIBO, diarrhoea, constipation, bloating, nausea, cramping
Itchy skin rash
Itchy watery eyes
Itchy ears
Brain fog
Flushing
MCAS Symptoms:
Rapid pulse (tachycardia)
Low blood pressure (hypotension)
Fainting (syncope) or dizziness
Itching (pruritus)
Hives (urticaria)
Swelling
Flushing
Wheezing
Shortness of Breath
Loud noise while breathing (stridor)
Diarrhoea
Nausea
Vomiting
Abdominal pain
Gastroesophageal reflux
Joint and bone aches
Other pain
Plus the histamine list above (if the mast cells are releasing histamine)
Is it possible to have both histamine intolerance and Mast Cell Activation Syndrome (MCAS)?
Yes, whilst the symptoms can be similar, you can have both histamine intolerance and mast cell activation syndrome. This is because excess histamine is present in both of these cases, and is causing symptoms.
If you find reducing high-histamine foods alone improves your symptoms, then you are much more likely to have histamine intolerance. You can easily find this out by following my 4-week Reboot meal plan program and downloading the free low-histamine food guide. A 4-week elimination diet is the gold standard test to find out if this may be your issue.
However – if you find you are also reacting to a few other random foods, e.g., herbs and spices or vegetables not listed as high histamine – you may have some mast cell activation going on. If your food options are shrinking, and you’re finding less and less tolerated foods, then mast cell activation is more likely.
You also may have mast cell activation if you find you have symptoms in response to changes in temperature, weather, stress, skin products, smells, etc.
I find most of my clients have a mix of histamine intolerance and mast cell activation. A low histamine diet is the first step in reducing the levels of histamine in the body and improving symptoms. After that, we work on the gut. Intestinal permeability is one potential issue, and underlying issues with bacteria triggering mast cells can often be one of the root causes of excess histamine. Also, learning how to calm and correct our overactive nervous system, which can also trigger mast cells to release inflammatory mediators into our body. We also correct nutritional deficiencies and improve detoxification. Ultimately changing our approach to food, our bodies, and our lives in order to bring health into every aspect of our wellbeing, and get back to enjoying life again!
About Luanne Hopkinson
Luanne Hopkinson (GradDipHumNutr, BSc, ADipNutrMed) is a clinical nutritionist, neuroplasticity coach, and founder of Happy Without Histamine. After navigating her own MCAS and histamine intolerance journey, she now helps women with MCAS and histamine sensitivity stop chasing triggers and start creating real healing.
Through her 5R Histamine Modulation Protocol™, Luanne combines gut microbiome repair with nervous system regulation to help the body feel safe again, so reactions settle, and life expands.
Because healing histamine intolerance isn’t about shrinking your world, it’s about getting back into it.
