An enigmatic allergic reaction at the dental office

This is the story of a 12-year-old boy referred to a pediatric pneumo-allergy department for suspected allergy to a local anesthetic during dental treatment. He has no history of allergies: no eczema, asthma, allergic rhinitis or conjunctivitis, or food allergies. Furthermore, he had previously received local anesthesia during dental treatment without ever experiencing a reaction.

At his dentist's office, the boy received local anesthesia using articaine, an anesthetic that is combined with adrenaline to prolong its effect. About twenty minutes after the procedure, he developed widespread hives, swollen lips, red eyes with swollen eyelids, throat discomfort, and vomiting. He was taken to emergency medical services about 20 minutes after the onset of the reaction, which was treated, among other things, by administering intramuscular adrenaline.

This young patient developed what is called grade 2 anaphylaxis, which is an allergic reaction with moderate involvement of at least two organs (skin, airways, digestive system). Symptoms disappeared about half an hour after the onset of the reaction.

The doctors then wondered what could have triggered this enigmatic anaphylactic reaction? Was it the anesthetic used? To be sure, they tested another product from the same family, lidocaine. But this test did not provoke any reaction, which ruled out a lidocaine allergy and therefore made articaine less suspect.

The allergists continued their investigation with a series of skin prick tests. Surprise: they found a positive reaction to latex. But when they repeated the test on undisinfected skin, the prick test result turned out to be negative. This alerted them: latex might not be the culprit… but rather the disinfectant used to clean the skin before the tests: chlorhexidine, an antiseptic widely used in medicine and dentistry to prevent nosocomial infections in the perioperative setting.

As the young patient's interrogation resumed, a previously unnoticed detail resurfaced: just before the local gingival anesthesia, the patient had used a mouthwash... containing chlorhexidine as an antiseptic! Neither the dentist nor the child had mentioned this. Neither had considered the mouthwash to be a medicinal treatment.

The doctors then performed a chlorhexidine prick test and took a blood sample to determine the level of IgE antibodies against the antiseptic. This time, the results were clear: the patient was indeed allergic to chlorhexidine.

It all makes sense: the chlorhexidine in the mouthwash entered the systemic circulation through the gap created in the gum during local anesthesia. It was therefore the antiseptic, during the perioperative period, that triggered the anaphylactic reaction in the dental office.

Published in April 2025 in the French Journal of Allergology , this clinical case highlights the need to conduct a systematic and exhaustive investigation in drug hypersensitivity assessments in order not to miss a rare cause. It is therefore important to systematically test all the drugs to which the patient has been exposed.

"Chlorhexidine is a cause of perioperative anaphylaxis that should not be overlooked. Its 'masked' presence in products used in the operating room or in dental care must be carefully sought and its involvement systematically explored during allergy assessments, including when the patient uses chlorhexidine without any problems on healthy skin or mucous membranes," conclude Eloïse Seigle-Ferrand and her colleagues from the Femme Mère Enfant hospital (Lyon civil hospices).

In this regard, the doctors discovered that after his dental treatment, the young boy had again used chlorhexidine, this time applying the antiseptic to the skin for small superficial wounds, without any reaction. The year before the anaphylaxis episode, he had also had a large superficial wound on his thigh, treated for several weeks with this same product, again without any problem.

Following this diagnosis of allergy to chlorhexidine, these Lyon clinicians contraindicate it, as well as any disinfectant product containing it, in the event of a skin or mucous membrane breach, and propose povidone iodine (betadine type) as an alternative.

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