Allergy is characterised by a local or systemic inflammatory response to allergens. Local symptoms are:
Nose: swelling of the nasal mucosa (allergic rhinitis)
The distinctive behavior known as nasal salute, also known as allergy salute, is the habit of wiping of the nose in an upward direction due to itching.
Eyes: redness and itching of the conjunctiva (allergic conjunctivitis)
Airways: bronchoconstriction, wheezing and dyspnoea, sometimes outright attacks of asthma
Ears: feeling of fullness, possibly pain, and impaired hearing due to the lack of eustachian tube drainage.
Skin: various rashes, such as eczema, hives (urticaria) and contact dermatitis.
Head: while not as common, headaches are seen in some with environmental or chemical allergies.
Systemic allergic response is also called anaphylaxis. Depending of the rate of severity, it can cause cutaneous reactions, bronchoconstriction, edema, hypotension, coma and even death.
Hay fever is one example of an exceedingly common minor allergy — large percentages of the population suffer from hayfever symptoms in response to airborne pollen. Asthmatics are often allergic to dust mites. Apart from ambient allergens, allergic reactions can be due to medications.