Which of the following is a common symptom of an allergic reaction?

Itchy, watery eyes are a hallmark symptom of an allergic reaction. This symptom occurs due to the body’s immune response to allergens, which triggers the release of histamines. Histamines can lead to inflammation and irritation of the eyes, resulting in itching and excessive tear production. This symptom is often seen in conditions such as allergic conjunctivitis or hay fever, where exposure to pollen, dust, pet dander, or other allergens activates the allergy response.

In contrasting this with the other options, miscommunication is not a physical symptom and does not relate to any physiological process of an allergic reaction. Unexplained weight loss is more indicative of other medical issues, such as metabolic disorders or malignancies, rather than an allergy. Constant fatigue can be associated with various conditions, but it is not a direct common symptom of an allergic reaction. Therefore, the correct answer focuses on the specific and direct effects of allergens on the body, which manifest as itchy, watery eyes.