Antihistamines commonly used to ease itching from atopic dermatitis do not deliver a large enough benefit for patients to clearly notice, a systematic review has found.
Histamine is a chemical substance released by mast cells that induces itching and skin inflammation. When it binds to receptors on skin nerves and cells, signals are transmitted to the brain, triggering intense itching. Consequently, antihistamines—which block histamine from binding to these receptors—have long been prescribed as an adjunctive treatment to reduce itching in atopic dermatitis.
In recent years, however, clinicians have urged caution against overprescribing these medications. Emerging research demonstrates that multiple proteins and inflammatory mediators beyond histamine can stimulate cutaneous nerve cells and trigger itching. As a result, antihistamines alone often fail to provide consistent relief while increasing the risk of adverse effects, including drowsiness, reduced concentration, and indigestion.
Actual treatment benefit falls short of perceptible threshold
Against this backdrop, a research team at McMaster University in Canada conducted a comprehensive analysis to quantify the real-world therapeutic benefits of antihistamines. The researchers reviewed 47 randomized controlled trials examining antihistamine use in patients with atopic dermatitis, encompassing a total of 6,230 patients. Their findings were published on July 29 in The BMJ.
After evaluating data across all 47 clinical trials, the team concluded that the therapeutic effect of antihistamines is too minor for patients to meaningfully perceive.
In clinical practice, the severity of atopic dermatitis is frequently evaluated using the objective SCORAD (oSCORAD) index, which scores disease extent and lesion severity on a scale from 0 to 83, with higher scores indicating greater severity. Patients taking second-generation antihistamines currently used in clinical practice saw their oSCORAD scores fall by an average of just 1.87 points. Because patients typically perceive clinical improvement only when scores drop by at least 8.2 points, the real-world effect of second-generation antihistamines reached only about 23% of the perceptible threshold.
The medications also failed to substantially relieve itching. On a 0-to-10 scale measuring itch intensity, second-generation antihistamines reduced scores by an average of 0.89 points—well below the 3-point reduction required for patients to feel a noticeable difference. Here as well, the reduction did not reach even 30% of the perceptible threshold.
Limited efficacy alongside persistent drowsiness risks
Because itching in atopic dermatitis stems from complex biological pathways beyond histamine alone, researchers noted that blocking histamine action in isolation cannot adequately control symptoms.
Side effect profiles also vary across drug classes. Older, first-generation antihistamines affect the central nervous system, causing drowsiness while impairing memory, reaction speed, and motor function.
Second-generation antihistamines do not eliminate sedating effects entirely. The study highlighted that cetirizine—the active ingredient in the widely used antihistamine brand Zyrtec—was associated with reports of drowsiness that were approximately 16 cases per 1,000 people higher than in the placebo group.
The findings do not imply that antihistamines are entirely unnecessary for all patients with atopic dermatitis. Individuals who also present with co-occurring allergic conditions, such as allergic rhinitis or hives, may experience relief from those accompanying symptoms. However, researchers emphasized that such benefits address concurrent allergic conditions rather than improving atopic dermatitis itself.
The research team concluded that, outside of managing specific co-existing allergic conditions, current evidence is insufficient to support the routine, daily use of antihistamines for atopic dermatitis.
