If a client has an allergic reaction during eyelash extension application, what should the practitioner do?

When a client experiences an allergic reaction during an eyelash extension application, the immediate and most appropriate action for the practitioner is to refer the client to a physician. This is essential because a physician can properly assess the severity of the allergic reaction and provide medical treatment if necessary. Allergic reactions can vary significantly in intensity, and while some mild reactions may be managed with over-the-counter remedies, it's crucial to ensure that the client receives appropriate care to prevent complications.

The other options may seem relevant but do not address the priority of professional medical assessment. Applying ice could provide temporary relief from swelling or discomfort, but it does not address the underlying allergic reaction. Continuing with the application is unsafe and potentially harmful, as it may exacerbate the reaction. Using antihistamines may offer some relief for mild symptoms, but without a physician's evaluation, it could overlook serious underlying issues needing immediate attention. Therefore, referring the client to a physician is the most responsible course of action in situations of allergic reaction during beauty treatments.