Skip to content


The MastAttack 107: The Layperson’s Guide to Mast Cell Diseases, Part 17

I answered the 107 questions I have been asked most in the last four years. No jargon. No terminology. Just answers.

25. How do I know what I will react to?
There is no way to definitively know what things will make you react. It is difficult to predict. There are some general guidelines many of us use to figure out what may be a problem but the only way to really know is to try something.
• Please note that because mast cell reactions are not known to be triggered by the same mechanisms as traditional allergies, you cannot exclude an entire class of drugs because you react to one in the way that you do for traditional allergies. This is particularly worth noting for opiates: reaction to morphine, for example, does not exclude fentanyl or hydromorphone.
• Mast cell reactions are not inherently triggered by IgE the way that “true” allergies are. This means that blood tests for IgE allergies will not identify triggers accurately for most mast cell patients. (Although some mast cell patients do have some IgE allergies.)
• Additionally, skin testing is wildly inaccurate in mast cell patients because of how reactive our skin is.
Stopping antihistamines is dangerous for mast cell patients.
Allergy testing is not accurate for mast cell patients.
• There are several ways that various things can cause mast cell reactions. Generally, they do it in one of the following ways: they cause mast cells to empty the chemicals in their pockets into the body (degranulation); they cause mast cells to release chemicals in another way; they already contain significant amounts of histamine; or the interfere with the mechanisms for controlling mast cell activation.
There are a number of medications that can cause mast cell degranulation or histamine release. Please note that not all of these medications are problematic for every patient. Only a provider managing your case can determine if these are safe for you or not. The major medications that may cause degranulation or histamine are listed below. This list is not exhaustive.

-Alcohol: Widely used to sterilize body area, surfaces, or tools; also used when preparing many medications that are not soluble in water
-Amphoterecin: Antifungal
-Aspirin: NSAID, for pain, inflammation, to block prostaglandins, to prevent clot formation
-Atracurium, mivacurium, rocuronium: Muscle relaxant
-Caine anesthetics (esters): Anesthetics, to numb
-Codeine, morphine, meperidine: Opiates, for pain or cough
-Colistin: Antibiotic
-Dextran: Volume expander, used in surgical or emergency situations to improve blood pressure
-Dextromethorphan: Cough suppressant
-Miconazole: Antifungal
-Nefopam: For pain
-NSAIDs (non steroidal anti-inflammatory drugs): For pain, inflammation, blocking production of prostaglandin
-Polymyxin B: Antibiotic
-Radioopaque contrast: To visualize structures in medical scanning procedures
-Reserpine: High blood pressure medication and antipsychotic
-Succinylcholine: Paralytic used for surgical procedures
-Thiopental: Anesthesia induction for surgical procedures
-Vancomycin (especially IV): Antibiotic

• There are a number of medications that are known to interfere with the mechanisms for controlling mast cell activation. Adrenaline is naturally made by the body to help control mast cell activation and other activities. When you interfere with the ability of adrenaline to act, it can potentially trigger mast cell activation. Drug classes that do this include beta blockers and alpha adrenergic blockers. This is particularly an issue if there is a history of anaphylaxis because these medications can interfere with Epipens.
Many foods either contain histamine or can trigger mast cell release of histamine. As with medication, you cannot exclude an entire family of foods because you react to one in the way that you do for traditional allergies.
• There are many lists of foods to avoid. They often conflict with each other. There is not yet a definitive list available. Despite this, there are some general rules of thumb that are agreed upon on what to avoid.
• Products that are fermented, contain alcohol, are overly ripe or leftover from previous days (especially meats), or contain dyes or preservatives are generally excluded.
• Beyond this, recommendations vary a lot more. Many diets recommend excluding yeast, citrus fruits, and nightshade vegetables.
Many activities inherently activate mast cells. Being too hot, standing or sitting in direct sunlight, exercise, sexual activities, menstruation, infection, and any type of physical trauma, even minor, can trigger mast cell activation as part of normal mast cell function.
Premedication is recommended for any medical procedure, even minor, as they can trigger mast cell activation.
• Patients may find that premedication prior to other activating activities is helpful for suppressing reactions.
Ultimately, the only way to know what is activating is through trial and error. Patients should consult their care team about what to trial, when, and how to make it as safe as possible.

For more detailed reading, please visit these posts:

Food allergy series: Mast cell reactions and the low histamine diet

The Provider Primer Series: Introduction to Mast Cells

The Provider Primer Series: Medications that impact degranulation and anaphylaxis

The MastAttack 107: The Layperson’s Guide to Understanding Mast Cell Diseases, Part 16

I have answered the 107 questions I have been asked most in the last four years. No jargon. No terminology. Just answers.

24. What is degranulation?
• Mast cells make chemicals inside them and often store them in pockets inside themselves. These pockets are called granules. When mast cells turn these pockets out so that the chemicals are dumped out of them into the body, that is called degranulation.
• There are several ways that mast cells release chemicals. These chemicals are commonly called mediators because they mediate many reactions in the body.
• Mast cells have to find certain building blocks from inside the body and whenever they find them, they use them to make mediators they need. Mast cells make some mediators whenever they have the opportunity and save them for later so they are there when they are needed. Often, the way mast cells save these mediators is by placing them inside granules. Mediators that are kept this way are called stored mediators.
• Mast cells have two options for getting those mediators out of their granules into the body. The first is to empty some of the granules entirely, just push everything out into the body at once. They can also release a little at a time. When mast cells are activated in response to an allergic or infectious process, overwhelmingly, they release the contents of a granule all at once.
Frequently, they empty many of the granules at the same time. This can cause an emergency response in your body and can impact your entire body. This is what happens during anaphylaxis but it happens during other processes too, like mast cell attacks, bad infections, or sudden trauma.
When mast cell patients say “I am degranulating”, it means they feel symptoms associated with mast cell mediator release. Histamine is stored in granules in large quantities so this is an offhand way of saying that they are feeling symptoms coming on.
• Mast cells have other ways of releasing mediators. They make some mediators only when they need to use them. These mediators are not stored but the building blocks they need are. A good example of this method is prostaglandin D2.
• Mast cells do not make prostaglandin D2 and stuff it inside granules. Instead, they keep the building blocks to make it inside of themselves. In this case, the building block they store is called arachidonic acid. When mast cells need to make prostaglandin D2, they use some of the arachidonic acid they have stored. But as soon as they use it to make prostaglandin D2, the mast cells secrete it right into the body. It is not stored in a granule.
• Mediators that are made with this kind of process are called “de novo” mediators. This means that the mediators are made “new” on demand when they are needed.



The effects of cortisol on mast cells: Part 2 of 3

Glucocorticoids, like cortisol, can affect mast cells in many ways. As I discussed in my previous post, there are many ways for mast cells to release mediators when activated. In all of these pathways, there are many molecules involved that carry the signal, like people passing the Olympic torch. In mast cells, one of the molecules that suppresses inflammatory activation signal is called SLAP (yes, really).  Cortisol increases the amount of SLAP in mast cells so inflammatory activation signals are suppressed.

An important step in degranulation is changing the amount of calcium inside the cell and moving it to different parts of the cell. In some studies, glucocorticoids can affect this movement of calcium. Other studies have found that in some pathways, glucocorticoids don’t affect calcium movement, but instead interfere with things like the IgE receptor.

Cortisol is also thought to directly inhibit stem cell factor (SCF) binding to the CKIT receptor. When SCF binds to the CKIT receptor, this sends a signal to the mast cell to stay live.  This means that taking glucocorticoids can let mast cells die at the appropriate time. SCF also tells mast cells to go to inflamed spaces.  By blocking this signal, glucocorticoids suppress inflammation.

One of the ways that molecules carry a signal is by changing the next molecule in the pathway. A big way that cells changing molecules is by chopping off a piece of them called a phosphate group.  This is done by special enzymes called phosphatases.  Glucocorticoids affect the availability of phosphatases so they aren’t able to get to the right part of the cell to carry the signal.  When this happens, there is less activation and less histamine release.

Arachidonic acid is the molecule modified to make eicosanoids (leukotrienes, thromboxanes and prostaglandins.) Glucocorticoids directly interfere with the production of these molecules in multiple ways.  The first way is by interfering with COX-2, one of the enzymes that makes prostaglandins.  Another way is by preventing arachidonic acid from being released to a place where they can be turned into leukotrienes, thromboxanes and prostaglandins.  This occurs because glucocorticoids increase the amount of a powerful anti-inflammatory molecule called annexin-I.  Annexin-I inhibits the molecule that releases the arachidonic acid, called phospholipase A2.

Annexin-I was the subject of an important paper earlier this year. In trying to identify exactly how mast cell stabilizers like ketotifen and cromolyn work, the researchers discovered that treatment with mast cell stabilizers decreased degranulation and increased annexin-I made by mast cells.  They also found that glucocorticoids had the same effect.


Oppong E, et al. Molecular mechanisms of glucocorticoid action in mast cells. Molecular and Cellular Endocrinology 2013: 380, 119-126.

Varghese R, et al. Association among stress, hypocortisolism, systemic inflammation and disease severity in chronic urticaria. Ann Allergy Asthma Immunol 2016: 116, 344-348.

Zappia CD, et al. Effects of histamine H1 receptor signaling on glucocorticoid receptor activity. Role of canonical and non-canonical pathways. Scientific Reports 2015: 5.

Coutinho AE, Chapman KE. The anti-inflammatory and immunosuppressive effects of glucocorticoids, recent developments and mechanistic insights. Mol Cell Endocrinol 2011: 335(1), 2-13.

Sinniah A, et al. The role of the Annexin-A1/FPR2 system in the regulation of mast cell degranulation provoked by compound 48/80 and in the inhibitory action of nedocromil. International Immunopharmacology 2016: 32, 87-95.

Mast cell mediator release mechanisms

There are many ways for mast cells to be activated.  Each of them involves a sequence of events involving several molecules.  These molecules change the next molecule in line in a way that causes it to perform a specific action.  It is hard to visualize and one of the harder concepts to understand about molecular biology.

I think of it like carrying the Olympic Torch to the Olympic Games. Before the Olympic Games, the Olympic Torch is lit in Greece.  Then a series of different people from all over the world carry the torch part of the way before giving it to another person.  Many, many people are involved, and the environment changes, but the torch always stays lit.  Finally, the very last person carries the torch into the stadium to light the Olympic Flame to open the Olympics.  Even though the people and environment changed, it’s still the same flame.

In the body, pathways are just like passing this Olympic torch. Instead of people carrying the flame and keeping it lit, molecules carry a message that they tell to the next molecule, and so on until the pathway ends.  The best known mast cell activation pathway is IgE activation.  IgE binds to a receptor on the outside of the mast cell.  The receptor knows that this means it has to degranulate.  It passes this message to a molecule, which passes the message down the line, just like the torch, until the mast cell degranulates.

Mast cells are well known for having many large granules that hold mediators until there is a signal to release. Granules are like pockets and mast cells stuff them full of premade mediators like histamine and tryptase. Mast cells actually sort mediators so that the granules are organized and mediators aren’t distributed randomly. The way mediators are stored together greatly affects the action of these molecules once they are released.

Large scale degranulation (sometimes called complete or anaphylactic degranulation) is the best known mast cell mediator release mechanism. In this kind of degranulation, granules swell and then lots of granules actually clump together to make a very large pocket. Then, this super pocket goes to the edge of the mast cell, the cell membrane, and pokes a hole to the outside.  The mediators in the super pocket are then released at once.  The granules and membrane have holes in them that will eventually be repaired. Following large scale degranulation, it takes about two days for normal mast cells to regranulate.

There is another kind of degranulation called piecemeal degranulation. This involves release of some mediators in a granule.  There is still a lot we don’t know about this process, but the general idea is that a regular granule puts some of its mediators into a tiny little bubble.  The little bubble then goes to the edge of the mast cell and slowly releases these mediators.  In piecemeal degranulation, the granules do not clump together to make one large granule, and there is no hole made in the membrane.  It is believed that some molecules help to push the mediators out of the cell but we don’t know what they are.

A number of mast cell mediators are not stored in granules and are instead made upon signals from specific pathways. Because these molecules aren’t stored in granules, it takes some time for them to be produced and released after mast cell activation. Lipid mediators, like prostaglandins and leukotrienes, are packed together and then transported across the membrane to the outside by other molecules.  Cytokines and chemokines are also produced on demand and then stored in small bubbles.  These small bubbles are then actively pushed out of the cell in a process called exocytosis.


Moon TC, et al. Mast cell mediators: their differential release and the secretory pathways involved. Front Immunol 2014: 5:569.

Wernersson S, Pejler G. Mast cell secretory granules: armed for battle. Nat Rev Immunol 2014: 14(7), 478-494.