Which of the following is a serious, potentially life-threatening reaction to allergens?

C. Anaphylactic Shock is a severe and potentially life-threatening reaction to allergens. This condition can occur very quickly after exposure to an allergen, such as certain foods, insect stings, or medications. Anaphylactic shock involves a dramatic immune response that can lead to symptoms like difficulty breathing, swelling of the throat, a rapid drop in blood pressure, and loss of consciousness. It requires immediate medical intervention, typically through the administration of epinephrine.

In contrast, asthma attacks, while serious and related to respiratory issues often triggered by allergens, generally do not have the same immediate life-threatening implications as anaphylactic shock. Allergic reactions can vary in severity; many are less severe and can include mild symptoms like rashes or itching. Acute rhinitis is primarily a nasal inflammation often linked to allergies, presenting with symptoms such as a runny nose or sneezing, but it is not typically classified as life-threatening. Therefore, anaphylactic shock stands out as the most severe and urgent allergic reaction.