Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic dermatitis, allergic asthma, and anaphylaxis. Symptoms may include red eyes, an itchy rash, sneezing, coughing, a runny nose, shortness of breath, or swelling. Note that food intolerances and food poisoning are separate conditions.

अधिहृषता या एलर्जी या "प्रत्यूर्जता" रोग-प्रतिरोधी तन्त्र का एक व्याधि (Disorder) है जिसे एटोपी (atopy) भी कहते हैं