Which of the following symptoms describes a severe allergic reaction?

A severe allergic reaction, also known as anaphylaxis, is characterized by both respiratory and circulatory symptoms that can be life-threatening. Diffuse wheezing indicates the presence of bronchospasm, which can significantly hinder a person's ability to breathe, while pharyngeal swelling can obstruct the airway, making it difficult for the individual to breathe sufficiency or even at all. This combination of symptoms indicates a systemic response to an allergen, requiring immediate medical intervention.

The other options reflect milder reactions to allergens, such as localized rashes, itching without swelling, or minor hives. These symptoms may be uncomfortable or concerning, but they do not indicate the urgent danger associated with a severe allergic reaction like anaphylaxis does. Therefore, the presence of diffuse wheezing and pharyngeal swelling is definitive of a severe allergic reaction that necessitates prompt and appropriate treatment.