Allergy

An allergy is an abnormal acquired sensitivity to a normally harmless substance which triggers a strong reaction from the immune system. Severe reactions result in difficulty breathing, severe rashes, swelling of the face or throat, dizziness, stomach upset or a drop in blood pressure and loss of consciousness.

Local symptoms include:

Nose – swelling of the nasal mucosa (allergic rhinitis)
Eyes – red, itching of the conjunctiva (allergic conjunctivitis)
Airways – sneezing, wheezing, constriction, asthma
Ears – feeling of fullness, ringing, impaired hearing or pain
Skin – eczema, hives (urticaria) and contact dermatitis
Head – headache

Systemic allergic response is called anaphylaxis which could affect the digestive system, respiratory system and circulatory systems.