Itching, redness, and swelling are often the primary symptoms of a skin allergic reaction, such as urticaria or contact eczema. To soothe these symptoms, antihistamines are frequently prescribed. Find out everything you need to know about this family of medicines in the following.
What should we know about antihistamines used to alleviate skin allergies?
Summary
Published on November 19, 2024, by Pauline, Chemical Engineer — 7 min of reading
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Antihistamines, what are they?
Available in the form of tablets, syrups, nasal sprays or even eye drops, antihistamines are medicines used to combat allergies, whether they are due to pollen, dust mites or even animal fur. The symptoms targeted by these medicines are numerous: they can include redness, swelling, itching, sneezing, a runny nose or even watery eyes.
Antihistamines allow for a relatively swift management of allergic symptoms. Indeed, while the onset of action varies depending on the type of medication and the severity of symptoms, antihistamines generally act within a few minutes to a few hours. Their effectiveness tends to persist for 24 hours. As soon as the allergic symptoms disappear, the treatment can be discontinued.
Note : There are two types of antihistamines, H1 antihistamines and H2 antihistamines. The former are used to alleviate allergies, while the latter are used to relieve certain gastric disorders. Only H1 antihistamines will be discussed in the remainder of this article.
What is the mode of action of antihistamines?
The effectiveness of antihistamines in alleviating allergic reactions is based on their ability to block histamine receptors, particularly in endothelial cells and sensory nerves. Indeed, in the event of an allergy, histamine, released by mast cells and basophils, binds to these receptors and triggers a cascade of inflammatory responses, responsible for the redness and itching characteristic of allergic skin reactions. To counter these effects, antihistamines themselves attach to the receptors, thus preventing them from binding to histamine.
This allows to reduce vascular permeability, a response induced by histamine that promotes the influx of fluid and immune cells to the affected tissues. By inhibiting this permeability, antihistamines alleviate the swelling of the skin and mucous membranes, thus reducing oedema and redness that appear during a skin allergy. Furthermore, they decrease the activation of sensory nerves, which limits the sensations of pain and the itching felt during an allergic reaction.
Antihistamines and Skin Allergies: What does the Scientific Literature Say?
The efficacy of antihistamines in combating skin allergies has been the subject of various studies, the conclusions of which are compiled in the table below. Overall, these studies demonstrate that these medications have a genuine benefit in alleviating redness, itching, and other allergic symptoms.
| Study | Dosage of the Antihistamine | Participants | Results |
|---|---|---|---|
| TENNSTEDT & al. (1990) | 10 mg of loratadine once a day or 60 mg of terfenadine twice a day | 30 patients suffering from chronic urticaria divided into 3 groups: loratadine, terfenadine and placebo | After 28 days, complete relief of symptoms was observed in 64%, 52%, and 25% of patients in the loratadine, terfenadine, and placebo groups respectively |
| TONET et al. (1999) | 10 mg once a day of mizolastine or loratadine | 247 patients suffering from chronic urticaria divided into 3 groups: mizolastine (88), loratadine (79), and placebo (80) | After 4 weeks, there was a significantly greater reduction in symptoms in the mizolastine and loratadine groups |
| LONG & al. (1999) | 20, 60, 120 or 240 mg of fexofenadine hydrochloride to be taken twice daily | 439 patients suffering from chronic urticaria divided into 5 groups: 4 different doses of fexofenadine and 1 placebo | After 4 weeks, there was a significantly greater reduction in itching in the fexofenadine groups (best results observed with 60 mg) |
| GEORGES & al. (2005) | 180 mg of fexofenadine hydrochloride to be taken daily | 255 patients suffering from chronic urticaria divided into 2 groups: fexofenadine (163) and placebo (92) | After 4 weeks, there was a significantly greater reduction in papules and itching in the fexofenadine group |
Efficacité des antihistaminiques utilisés en cas d'allergie cutanée.
In the event of the antihistamines' inefficiency in combating a skin allergic reaction, it is possible to resort to corticosteroids, calcineurin inhibitors, or even leukotriene inhibitors. The key is to consult a doctor who will guide the patient towards the solution most suited to their situation.
What are the side effects associated with taking antihistamines?
Antihistamines are generally well tolerated. This is particularly true for second-generation ones, such as bilastine or cetirizine, which pose almost no risk of side effects. However, when it comes to first-generation antihistamines, like chlorphenamine or diphenhydramine, they are quite commonly associated with risks of drowsiness. This type of antihistamine is preferably taken in the evening, before sleeping. First-generation antihistamines can also have an anticholinergic effect, meaning they can block peripheral cholinergic receptors. This can lead to a dry mouth sensation, urinary retention, headaches, or even tachycardia. This last side effect, however, is quite rare.
Most commonly, the side effects of antihistamines are linked to an overdose, hence the importance of strictly adhering to the dosages prescribed by healthcare professionals.
Sources
FEINBERG S. The antihistaminic drugs: Pharmacology and therapeutic effects. The American Journal of Medicine (1947).
SEEVERS M. & al. The toxic effects of anti-histaminic drugs. Journal of the American Medical Association (1951).
PEARLMAN D. Antihistamines: pharmacology and clinical use. Drugs (1976).
TENNSTEDT D. & al. Comparative effects of loratadine and terfenadine in the treatment of chronic idiopathic urticaria. Annals of Allergy (1990).
LONG J. & al. A double-blind, placebo-controlled trial of fexofenadine HCl in the treatment of chronic idiopathic urticaria. The Journal of allergy and clinical immunology (1999).
TONET J. & al. Efficacy and safety of mizolastine 10 mg in a placebo-controlled comparison with loratadine in chronic idiopathic urticaria: results of the MILOR Study. Journal of the European Academy of Dermatology and Venereology (1999).
SIMONS K. & al. Clinical pharmacology of H1-antihistamines in the skin. Journal of Allergy and Clinical Immunology (2002).
GEORGES G. & al. Once-daily fexofenadine treatment for chronic idiopathic urticaria: a multicenter, randomized, double-blind, placebo-controlled study. Annals of allergy, asthma and immunology (2005).
