Allergies - Symptoms 

Symptoms of allergies 

Media last reviewed: 01/11/2012

Next review due: 01/11/2014

Allergic reactions do not happen the first time you come into contact with an allergen, but at a later point of contact.

This is because the body’s immune system has to develop sensitivity to the allergen before you can become allergic to it. In other words, your immune system needs to recognise and memorise the allergen (for example, pet hair or pollen) and then make antibodies against it. This process is known as sensitisation.

The time taken to become sensitised to an allergen varies from days to years. Some people stop in the sensitisation phase, experiencing symptoms but never fully developing an allergy to the allergen.

Typical allergic reactions involve irritation and inflammation (swelling) in the body. Symptoms may include:

  • sneezing
  • wheezing
  • sinus pain (pressure or pain high up in the nose, around the eyes and at the front of the skull)
  • runny nose
  • coughing
  • nettle rash (hives)
  • swelling
  • itchy eyes, ears, lips, throat and palate (roof of mouth)
  • shortness of breath
  • sickness, vomiting and diarrhoea

It is important to remember that these symptoms can also be caused by other conditions, so see your GP for advice if you're not sure what's causing your symptoms.


In very rare cases, an allergy can lead to a severe allergic reaction called anaphylactic shock, which can be fatal.

Most allergic reactions occur locally in a particular part of the body, such as the nose, eyes or skin. In anaphylaxis, the allergic reaction involves the whole body and usually happens within minutes of coming into contact with a particular allergen.

The symptoms of anaphylactic shock can include any or all of the following:

  • swelling of the throat and mouth
  • difficulty swallowing or speaking
  • difficulty breathing
  • a rash anywhere on the body
  • flushing and itching of the skin
  • stomach cramps, nausea and vomiting
  • a sudden feeling of weakness due to a fall in blood pressure
  • collapse and unconsciousness

You can read up on anaphylaxis for more information on a severe allergic reaction. If you have anaphylactic shock, you will require emergency treatment, usually with an injection of a medicine called adrenaline.

Page last reviewed: 23/03/2012

Next review due: 23/03/2014


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