Allergy is an altered immune response to a substance which is eaten, inhaled or injected and which is harmless in most people. Substances (allergens) as diverse as pollen, penicillin and bee venom produce reactions which vary in severity from a mild rash or itching/sneezing to bronchial asthma and, occasionally severe, life-threatening anaphylactic shock (see entry, Anaphylaxis).

In principle any substance can cause an allergy. Common ingested allergens include peanut, fish, eggs and milk. Injected substances include drugs (antibiotics) and insect venom (wasp stings). Inhaled allergens which may cause rhinitis and asthma include house dust mite, pollens and animal danders. Common skin sensitisers include latex and house dust mite. Occupational allergy includes asthma, rhinitis or dermatitis which occurs following exposure to a particular substance in the work place.

Diagnosis of allergies is usually straightforward although it may sometimes be difficult and time consuming. In general, there is a period of exposure prior to development of symptoms during which sensitisation occurs. Only a proportion of sensitised (atopic) people go on to develop symptoms (allergies) following re-exposure to the allergen. For example, egg and milk allergy commonly occur in infancy when exposure to these foods is most common. Allergic asthma occurs later in childhood following exposure to inhalant allergens including house dust mites and animal danders, whereas hayfever peaks in adolescence/early adulthood following repeated exposure to seasonal pollens, the 'Allergy March.'

Food allergy characteristically presents with multiple symptoms (lip swelling, tightness in the throat, rhinitis, abdominal pain, nettlerash and/or asthma and, rarely, life-threatening anaphylaxis). Rhinitis presents with itch/sneezing, watery nasal discharge and associated eye symptoms during the pollen season. Allergic asthma presents with cough, sensation of tightness in the chest, wheeze and breathlessness.

There is a history of immediate symptoms on exposure to these allergens and sensitivity may be confirmed either by skin prick testing with the relevant allergen and/or a blood test which measures the level of allergy-related IgE antibodies in the blood to the relevant allergen. However, these tests must always be interpreted in the context of a patient's symptoms on exposure to the relevant allergen, otherwise false-positive tests will occur. Occasionally, there is no particular time relation between exposure and symptoms so diagnosis may be difficult. Also, spontaneous remission may occur.

Diseases which may be caused or aggravated by allergy include:

• Asthma
• Hayfever/rhinitis
• Conjunctivitis
• Acute urticaria (nettlerash, hives) - Chronic urticaria, however, is frequently not due to an allergy
• Food allergy
• Drug allergy
• Venom allergy
• Anaphylaxis

Inheritance patterns
Allergy is commonly, although not always, associated with a family history of allergic disorders. The likelihood of allergy is greater if one or both parents have an allergy.

Prenatal diagnosis
None, although a family history in both parents is very commonly associated with allergic manifestations in offspring.

Medical text written November 1991 by Contact a Family. Approved November 1991 by Dr J Brostoff, Consultant Immunologist, Middlesex Hospital, London UK. Last updated July 2002 by Professor S R Durham. Last reviewed May 2006 by Professor S R Durham, Professor of Allergy & Respiratory Medicine, Imperial College, London, UK.

Further Online Resources
Medical texts in The Contact a Family Directory are designed to give a short, clear description of specific conditions and rare disorders. More extensive information on this condition can be found on a range of reliable, validated web sites and links to them are included in the CD-ROM version of this Directory. Further information on these resources can be found in our Medical Information on the Internet article.

Allergy UK
3 White Oak Square
London Road
Swanley
BR8 7AG
Tel: 01322 619898
Fax:01322 663480
e-mail: info@allergyuk.org
Web: http://www.allergyuk.org

Allergy UK is a National Registered Charity No. 1104845, established in 1991. It offers: information, advice and support to people with allergies; details of NHS allergy clinics and allergy specialists; and translated cards for people who are travelling abroad identifying the carrier as having a serious allergy and providing emergency information. Activities include raising awareness among doctors, nurses, pharmacists, health visitors and dieticians by way of advanced training to diploma and degree level. It has a wide range of information available, details on request. Allergy UK receives over 40,000 enquiries a year. They also run Web: http://www.blossomcampaign.org which offers advice and information for parents and children regarding social exclusion of children due to allergies.

Group details last updated August 2007.

ACTION AGAINST ALLERGY

Action against Allergy
PO Box 278
Twickenham
TW1 4QQ
Tel: 020 8892 2711
e-mail: AAA@actionagainstallergy.freeserve.co.uk
Web: http://www.actionagainstallergy.co.uk

The organisation is National Registered Charity No. 276637. It offers: access to a telephone support network; and co-ordination of an Allergy information centre and library. A specialist referral service provides contact details for NHS and private allergy specialists. It publishes a newsletter three times a year and has a wide range of information available, details on request. The organisation has approximately 2,000 members.

Group details last confirmed January 2007.

Latex Allergy Support Group
PO Box 27
Filey
YO14 9YH
Mob 07071 225838 (Mon-Fri, 7pm - 10pm)
e-mail: latexallergyfree@hotmail.com
Web: http://www.lasg.co.uk

The Group is a National Registered Charity No. 1104845, established in 1996. It supports affected individuals and their families and raises awareness amongst the public, healthcare workers, schools and other at risk groups. It publishes a quarterly newsletter, 'Bouncing Back' and has information available, details on request.

Group details last confirmed Spetember 2007.