Symptoms of allergies 

The symptoms of an allergic reaction can vary, depending on which substance (allergen) you are allergic to.

If you are allergic to substances in the air – such as pollen, animal dander and dust mites – the symptoms usually include:

  • rhinitis  sneezing and a blocked, itchy or runny nose
  • conjunctivitis  itchy, red, streaming eyes
  • asthma  wheezing, breathlessness and a cough

If you are allergic to a certain food or medication, symptoms can include:

You can also be allergic to substances coming into direct contact with the skin, such as perfumes, soaps, hair dyes and metal jewellery. This causes a type of eczema known as contact dermatitis.

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.


The symptoms of an allergic reaction 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, as they experience symptoms, but never fully develop an allergy.


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
  • collapsing and becoming unconscious

You can read about 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.


Find out about the symptoms of allergies, how they're treated, and how allergic reactions can be avoided

Page last reviewed: 01/04/2014

Next review due: 01/04/2016