Allergy is an abnormal body reaction characterised by an exaggerated response upon coming into contact with an external substance to which other individuals normally do not react. These substances are called allergens.

Allergic reactions can provoke lacrimation (tearing), eye itching, reddening of the eye (conjunctivitis) sneezing, nasal congestion, nose itching, runny nose (rhinitis), cough, suffocation, and chest wheezing (asthma).

People can be allergic to many different agents, though the most common allergens are usually pollen, mites in house dust, moulds, the epithelia of domestic animals , and some products for professional use such as latex.

Allergy is sometimes confused with a common cold or sinusitis. The following are the most common symptoms of an allergic person:

			The appearance of symptoms is closely associated to exposure to the causal agent (pollen in spring, epithelia e.g., hair and fur of animals, etc.).
			Nose plugging, alternating from one side to the other.
			Affected people catch colds characterised mainly by itching and sneezing with lacrimation.
			The secretions are watery and transparent.