Allergy : an abnormal reaction of the tissues to certain substances ‘allergens’ ‘antigens’ capable of making the body produce antibodies..
AetiologyMechanism of allergy(3phases):1. IgE (formed by lymphocytes). 2. IgE is bound allergen and to mast and basophil cells, initiates the secretion of substances such as histamine that lead to the clinical manifestations.3. Capillaries become permeable, and oedema occurs. Eosinophils infiltrate the tissues. Serous alveolar glands are stimulated either directly or via an autonomic reflex to produce excess watery secretion.Predisposing factors1. hereditary.. ‘Atopy’=inherited tendency.2. physical: Changes in the humidity/ pollution
Precipitating factors
1. Exogenous. from outside the body . a.Inhalants: ,: dusts, pollens,animal,feathers,fungal spores and the house-dust mite b.Ingestants; (foods): especially in children such as eggs, strawberries, nuts or fish .Milk or wheat are less obvious. c.Contacts to skin or nasal mucosa;. Face powders, and hair from electric razors, nasal drops or sprays . d.Drugs ; nasal symptoms may be part of a more generalized allergic response. e.Infection: bacterial ,fungi and parasites allergy has been suspected but never proved. 2. Endogenous; tissue proteins (from injured tissues, transudates and exudates) ..Clinical types 1.Seasonal ('hay-fever'). 2.Non-seasonal (perennial). Age incidence any age less common after 50 years of age.
Diagnosis 1.Careful history. 2.Clinical examination..3. Eosinophils. May be found in great numbers in the nasal secretions ,the nasal mucosa or polypi. The eosinophil count of the blood is raised, especially in the morning, and always in the presence of an extrinsic allergen. 4. Skin tests. These are confirmatory. Sensitivity is less than 50% of cases clinically suggestive of a non-seasonal allergy. Nearly all patients with seasonal symptoms will give positive responses. 5. intranasal test. A drop of test solution may promote rhinorrhea and sometimes lacrimation - so-called 'nasal provocation' test. 6. Elimination test. may be helpful, especially in suspected food allergies.