If you live with systemic mastocytosis (SM), taking an antihistamine may be part of your daily routine. But how much do you know about what it actually does?
Understanding how antihistaminesAntihistamines Medications that block the effects of histamine, the chemical found in mast cells that is responsible for many of the symptoms of SM, as well as many allergic reactions. work in your body can help you understand which SM symptoms they are likely to help with.
Why histamine causes symptoms in mastocytosis
Histamine is a natural chemical stored mainly inside your mast cells. It’s one of the chemicals that mast cells release during allergic reactions — and it’s what drives the itching, redness and swelling of a typical allergy.
In SM, your body makes and stores too many mast cells. When they are activated, more histamineHistamine A chemical released by mast cells when they are activated. Histamine causes many of the allergy-type symptoms in mastocytosis, including flushing, itching and hives. than usual is released into the surrounding tissue. That’s why flare-like symptoms such as hives, flushing and stomach upset can appear suddenly.
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How antihistamines work
This is where antihistamines come in. They don’t lower your mast cellMast cell A type of white blood cell produced in the bone marrow. They help defend against infections and play a key role in allergic reactions. In SM, mast cells become overactive and build up throughout the body. count, and they don’t stop your mast cells from releasing histamine. Instead, they block histamine that has already been released from attaching to receptors on your cells, which keeps it from triggering symptoms.
Histamine causes such a wide range of symptoms because it acts on more than one kind of receptor, and the effect you feel depends on which one it attaches to. Two of these receptors, called H1 and H2, are the primary targets covered by antihistamine medications, and treatment for SM often uses both types together.
Read more about SM signs and symptoms
H1 antihistamines
H1 antihistamines block H1 receptors and are used mainly to prevent flushing and itching — the skin symptoms many people with SM notice first. They come in two generations:
- First-generation options (such as diphenhydramine or hydroxyzine) work well but more often cause drowsiness.
- Second-generation options (such as cetirizine, loratadine or fexofenadine) tend to be less sedating, which matters if you take them daily.
H2 antihistamines
H2 antihistamines block H2 receptors in the stomach lining and mainly ease gastrointestinal symptoms such as reflux and stomach discomfort. (If you take a proton pump inhibitor for reflux, it works differently and does not replace your H2 antihistamine.)
Commonly used options include:
- Famotidine.
- Cimetidine.
- Nizatidine.
What else should patients know?
Using both types of antihistamine together lets you target a broader range of symptoms than either alone, which is why H1 and H2 antihistamines are a foundation of symptom control across both skin and digestive symptoms.
A couple of practical points worth keeping in mind:
- Doses used in SM may be higher than a standard allergy dose, so follow your prescriber’s instructions rather than the package label.
- Long-term use of some antihistamines has been linked to cognitive effects, so it’s worth telling your doctor about any new problems with your concentration, memory or thinking.
Working with your SM care team
Antihistamines are just one aspect of a broader SM treatment landscape. Keeping a simple symptom diary — noting what you took and how you felt — gives your care team the detail they need to fine-tune your treatment plan.
