An allergy is an immune response to typically harmless substances in the environment such as pollen or dust, with symptoms that may include sneezing, a stuffy nose and itchy eyes.
WHAT IS AN ALLERGY?1, 2
Allergy occurs when a person’s immune system reacts to substances known as allergens in the environment that are harmless for most people.3
When a person who is allergic to a particular allergen comes into contact with it, an allergic reaction occurs. This begins when the allergen (for example, pollen) enters the body, triggering an antibody response.
The antibodies attach themselves to special cells, called mast cells. When the pollen comes into contact with the antibodies, the mast cells respond by releasing certain substances, one of which is called histamine. When the release of histamine is due to an allergen, the resulting swelling and inflammation is extremely irritating and uncomfortable.3
Common allergy triggers2,3,5
The substance that triggers an allergic reaction is called an allergen. These include:
- Animal dander – tiny specks of shed animal skin
- Pollen from trees, flowers, grass and weeds
- Dust mites, which are tiny insects commonly found in pillows, mattresses, carpets and upholstered furniture
- Mould – fungi found indoors and outdoors
- Certain foods, medicines and chemicals
- Venom from insect bites
ALLERGIES AND THE IMMUNE SYSTEM1,2
The primary function of the immune system is to defend the body from disease-causing organisms such as viruses and bacteria, resulting in an inflammatory response. Similarly, allergic subjects exposed to allergens develop allergic inflammation as part of the allergic reaction with associated unwanted side effects which can vary in severity.1,2,3
SYMPTOMS: WHAT TO LOOK OUT FOR2,5
The different stages of an allergic reaction
Early Phase Response Stage
A substance called histamine is one of the mediators released within minutes of being exposed to the allergen. These mediators are responsible for some of the general symptoms associated with allergic rhinitis such as sneezing, itching, a runny nose, watery eyes, swelling or nasal congestion. This also mediates inflammation.
Late Phase Response Stage
After 4 to 6 hours of exposure to the allergen, tissues become red and swollen due to the arrival of other inflammatory cells to the area e.g. eosinophils, macrophages, basophils.
Common allergic symptoms4,5
An allergic reaction can affect any part of the body. However, the skin, nose, eyes and lungs are mainly affected.
Early phase response of exposure to an allergen may include:
- Blocked or runny nose and sneezing
- Red, watery and itchy eyes
- Coughing and/or difficulty breathing
- Itchy skin with or without a skin rash
Allergic skin conditions include rashes, itchy patches (urticaria / hives), insect bites or stings and eczema.
Insect bites or stings7
Identifiable by the redness and swelling around the sting area, which for most people goes away after a while, insect bites or stings are mostly caused by bees and wasps. Some people have almost no reaction while others have an extreme allergic reaction (anaphylactic shock), which can be life-threatening.7
Eczema (atopic dermatitis)6,9
Atopic dermatitis is the most common form of eczema and is mostly caused by allergens. Showing up as itchy, dry patches it can affect the entire skin or specific areas only such as arms, legs, face or neck, and the area affected may become infected.
Allergies caused by inhaling allergens such as animal dander, pollen and dust mites lead to nasal congestion, nasal discharge, sneezing and inflammation.
When caused by an allergy the inflammation of the nasal cavity is called allergic rhinitis. There are two types of allergic rhinitis. Perennial allergic rhinitis occurs year-round while the seasonal kind occurs at the time of year when plants, flowers and trees pollinate.
Allergic rhinitis causes the nose to become blocked, which in turn blocks the sinuses – the cavities located near the eyes behind the nose.
Various conditions can cause sinusitis, including the common cold but when the nasal and sinus cavities become inflamed due to allergy it is called rhinosinusitis.
In other words, allergic rhinitis can lead to sinusitis.
ALLERGY DIAGNOSIS AND TREATMENT4,7
While there is no guaranteed cure for allergic reactions, the symptoms can be:
- Prevented to a certain extent by reducing exposure to allergens
- Managed or modulated with treatments that adjust the immune system’s response to perceived ‘invaders’
Steps to reduce exposure to allergens4,7
Avoid exposure to triggers by allergy-proofing your environment and encouraging behavioural changes as follows:
- Make use of air conditioning
- Invest in bed linen and sprays that combat the presence of bed and dust mites
- Ensure that there are no visible signs of mould in your living spaces at home
- Wash hands after handling or petting animals
Treatment options 2,7,8,10
Allergies can make the simplest activities difficult so it is important to get the best symptom control possible.
- Antihistamines – rather than stopping histamine production, which is an important part of your defensive system
- Decongestants come in the form of tablets or sprays and help clear nasal congestion for easier breathing
- Topical medications that are readily available
- Corticosteroids taken orally or as a nasal spray help reduce inflammation throughout the body
- Immunotherapy desensitises the immune system to allergens and is used for severe allergies that cannot be relieved by other methods of treatment
Amy E. Thompson, MD, The Immune System, JAMA April 28, 2015 Volume 313, Number 16 https://jamanetwork.com/journals/jama/fullarticle/2279715 Stephen J. Galli, The development of allergic inflammation, NIH Public Access Author Manuscript, Feb 15, 2013 https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3573758/ Australian Society of Clinical Immunology and Allergy, What is Allergy, 2017 https://www.allergy.org.au/images/pcc/ASCIA_PCC_What_is_allergy_2017.pdf J.Sheldon, Allergy Diagnosis Reference Guide, Clinical Biochemistry, East Kent Hospitals University, Bio No 116, October 2014 https://www.mtw.nhs.uk/wp-content/uploads/2015/08/Allergy_diagnosis_reference_guide.pdf Ramírez-Jiménez F, Allergic Rhinitis, Journal of Allergy & Therapy, 2012 https://www.omicsonline.org/allergic-rhinitis-2155-6121.S5-006.pdf Delaware Health and Social Services, a Division of Public Health, Rashes and Skin Irritations, Frequently asked Questions, Sept 9, 2009 https://www.dhss.delaware.gov/dph/files/rashesfaq.pdf Australian Society of Clinical Immunology and Allergy, Allergic Reactions to Bites and Stings, 2015 https://www.allergy.org.au/images/pcc/ASCIA_PCC_Allergic_reactions_bites_stings_2016.pdf National Institute for Health and Care Excellence, Drug Allergy: Diagnosis and Management, Clinical Guideline, Sept 3, 2014 https://www.nice.org.uk/guidance/cg183/resources/drug-allergy-diagnosis-and-management-pdf-3510981102282 Contact dermatitis/Eczema: Link: https://www.allergy.org.au/images/pcc/ASCIA_PCC_Eczema_2015.pdf ASCIA. Australia and New Zealand. Eczema (Contact Dermatitis). 2015. Contact dermatitis/Eczema: Link: https://www.allergy.org.au/images/pcc/ASCIA_PCC_Eczema_2015.pdf ASCIA. Australia and New Zealand. Eczema (Contact Dermatitis). 2015.