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An allergy is an immune-system disorder characterised by an exaggerated response to external elements, known as allergens, that are harmless to most individuals. These can be pollen, mould, animal hairs, foods, wasp or bee stings, and medications. This disorder may manifest in isolation in the respiratory (hay fever, asthma), abdominal or cutaneous systems, or, in severe cases, in multiple organs and systems.



They may appear in isolation in respiratory, abdominal or cutaneous systems, depending on the route of exposure to the allergens (respiratory, ingestion, etc.,) and cause various illnesses such as asthma. In severe cases, reactions may lead to combined symptoms in several organs and systems and cause a life-threatening condition called anaphylaxis.

Depending on the area affected, there may be:

  • Respiratory symptoms: itchy nose and eyes, nasal obstruction, runny nose, difficulty breathing, a sensation of a foreign body in the throat, wheezing and coughing. 
  • Digestive symptoms: abdominal pain, diarrhoea and vomiting.
  • Skin symptoms: appearance of hives (raised, red welts on the skin) –either scattered or generalised – over the whole body.

In the event of a systemic reaction (anaphylaxis) the symptoms mentioned above have the tendency to appear all together within the first hour of exposure to the allergen, and these may also be accompanied by a feeling of dizziness and fainting that require urgent medical attention and medication.


Who is affected by the condition?

The WHO classes allergic disease as one of the six most common afflictions in the world. It is estimated to affect up to 20% of the world’s population, with developed and industrialised countries affected the most.

Here in Spain, it is estimated that one in four people may suffer some kind of allergic disorder in their lifetime. Nevertheless, there are notable differences in the frequency of presentation of the various allergic diseases in our country's geographic regions. Bronchial asthma, for example, is more common in the coastal and island areas than in the centre of the peninsula, with a prevalence that ranges between 1% and 5% of the general population. By comparison, the European average is 6%.

There are no definitive data available on the frequency of the various allergic diseases, given the disparities between the results of the various studies conducted. However, we do have reliable data on the reasons for the consultations made by Spanish patients with allergists: hay fever (allergic rhinitis), asthma and allergies to medications occupy the top three spots, with a frequency of 54%, 23%, and 17%, respectively.

Hay fever is the most common affliction, affecting up to 21% of the general population in Spain, even though there are, as with asthma, notable differences between geographic areas. Atopic dermatitis is the next most frequent, affecting 4% of school-aged children. Lastly, food allergies affect 3-5% of the paediatric population, but less than 2% of adults.

The second half of the 20th century saw a spectacular rise in allergy numbers , multiplying fivefold in developed countries. It seems, however, that the trend over the last decade has reached a plateau, and a slight decrease has even been observed.



Allergy tests are used to identify the substances a patient is sensitised to. This study is based on the use of skin tests, laboratory tests to study the presence of antibodies against the suspected allergens and controlled exposure to these allergens.

In the case of allergic respiratory diseases, such as hay fever or asthma, a precise measurement can be made of a patient is affected through safe, painless techniques such as spirometry, the exhaled nitric oxide test and acoustic rhinometry. There are other diagnostic tests of uncertain or untested value whose results should be interpreted with caution and with our current scientific knowledge taken into account. In any case, the allergist should always be the professional who prescribes and evaluates all these tests.


Typical treatment

The treatments available for allergic disorders vary depending on their characteristics, the severity of the allergies and whether they focus on alleviating symptoms or curing the condition:

  • Symptomatic treatment: There are effective pharmacological therapies to treat the symptoms of allergic diseases. Prevention therapies can also be carried out or safe alternatives sought in the case of drug allergies. 
  • Disease-modifying treatment: When the symptoms are only being partially controlled or not controlled at all, and the diagnostic tests identify a clear trigger, the patient can opt for disease-modifying treatments that aim to increase their tolerance threshold for the allergens. These treatments can lead to improvements in the symptoms and a reduced need to use medications to alleviate symptoms. 



There are currently no specific recommendations for preventing the appearance of this disease. In the specific case of food allergies, it has been observed that the early introduction of foods that are traditionally considered “allergens”, from 4-6 months of age onwards (keeping in mind the psychomotor and digestive development of babies), can reduce their risk of developing allergies.

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