The asthma and allergy team at Royal Brompton and Harefield hospitals has a national and international reputation for excellence, ground-breaking research, and developing asthma and allergy treatments.
Consultant dietitian and clinical lead for food allergy at the hospitals, Dr Isabel Skypala, explains what allergies are, how patients with allergies can be treated and the difference between food allergies and intolerances.
What are allergies and why do people develop them?
An allergy is an abnormal response of the immune system to a harmless substance, such as food, pollen, or animals. An antibody called Immunoglobulin E (IgE) is produced by the immune system to protect the body from disease causing organisms such as parasites. However, in people with allergies, when IgE antibodies meet a harmless substance a reaction occurs that was originally designed to destroy harmful organisms and instead causes the symptoms of an allergy.
This reaction involves the release of substances, including histamine, which cause the classic symptoms of an allergy. These symptoms can be related to:
- the skin, such as flushing, itching, swelling, and hives;
- the gut, such as abdominal pain, vomiting, and diarrhoea;
- the lungs, such as wheezing and breathlessness;
- the heart, such as palpitations and light-headedness.
More severe reactions, such as those involving the lungs or heart, are often described as anaphylaxis and will require emergency care.
It is not always clear why people develop an allergy, although the risk is higher if one or both parents have allergies. Allergies are also becoming more common, affecting more than 1 in 4 people in the UK.
Can an allergy ever appear or disappear in adulthood?
Allergic conditions usually start in childhood, for example, most nut allergies start in childhood. However, allergies can also begin or disappear in adult life, such as with hay fever that develops in adults and asthma that can disappear in adults after having suffered with it as a child. Food allergies are another example of this, allergies to some foods like milk, egg, wheat and soy often start in childhood but are then resolved in adolescence or early adulthood. Whereas allergies to foods such as shellfish or fruit may only appear in adult life.
Some types of food allergies are also linked to other allergies. For example, a common food allergy called pollen food syndrome, or oral allergy syndrome, is actually linked to pollen. People with oral allergy syndrome are allergic to tree pollen but also have a mild allergic reaction in the mouth and throat when certain raw fruits, vegetables or nuts are eaten. This is because there is a protein in birch tree pollen that is similar to a protein found in some fruits and vegetables, including apples, peaches and kiwi, and the antibodies against tree pollen recognise and react to these foods. Around 2 per cent of adults in the UK suffer from this allergy.
How do doctors diagnose allergies and how are allergy patients treated?
It depends on the type of allergy, but there are four types of allergy tests:
- Skin prick testing: This is where a small prick into the skin is made on the forearm using a pin that has a common allergen on it in a liquid form. If allergic to the substance, a small red bump will develop on the skin where the prick was made.
- Specific IgE blood test: This measures the amount of IgE antibodies within the blood against a particular food, pollen, animal, or insect that is known to cause allergies.
The problem with this test is that lots of people make IgE antibodies when coming contact with a substance, but do not actually react to it and develop allergic symptoms. Having IgE antibodies but not developing an allergic reaction is called being sensitised to the food, pollen, or other allergen and is quite common. That takes us to the third test:
- Component-resolved diagnosis: This involves testing for individual proteins found in a food. For example, there are some proteins in peanuts that are linked to a peanut allergy and some that are linked to pollen allergy. Testing for these individual proteins can therefore help determine if patients are allergic to peanuts or are having an allergic reaction when eating peanuts because they are allergic to pollen. This specialist test is usually only available in hospital allergy clinics.
And lastly:
- Food and drug challenges: This is the gold standard test to diagnose a food or drug allergy. This test is usually performed as a day case under strict medical supervision with the food or drug being given in increasing amounts.
Once an allergy has been diagnosed it can be treated. Topical creams such as steroid creams are usually recommended for active eczema, but it is also important to make sure the skin does not get dry by using regular emollients. Antihistamines are sometimes used to treat skin symptoms but are mainly used is in the treatment of hay fever, although nasal sprays containing locally absorbed steroids are also important for optimal management. Inhaled steroids are also the mainstay of asthma management, with other drugs being added if symptoms are not well controlled.
Allergen avoidance is key in managing allergies, although more severe allergic reactions often require antihistamines, steroids and even adrenaline. Longer term options include desensitising the immune system (e.g. immunotherapy and ‘biologic treatments’).
What is the difference between food allergies and food intolerances?
Food allergies involve IgE antibodies, whereas food intolerances may not involve the immune system at all. People with food allergies will react within 1–2 hours of eating, have typical allergic symptoms, such as a rash, itching or swelling, and usually a positive IgE or skin prick test to the food.
People with food intolerances often have delayed symptoms, which might not be typical of an allergy, and usually have a negative IgE test to the food. Also, people may not always react to the trigger, sometimes a certain amount of the food, or a particular form of the food, need to be eaten to have a reaction. Food intolerances can be caused by a lack of an enzyme to digest the food – for example, lactose intolerance.
Why did you want to specialise in allergy medicine?
I have always been interested in allergies from the start of my career. As an undergraduate dietitian, my final dissertation was on food allergy and asthma. When I started at Royal Brompton Hospital, I worked with Professor John Warner to set up a food allergy service for children, and with Professor Stephen Durham to establish a food allergy service for adults. I have always had fantastic support from my medical allergy colleagues, who embrace a truly multi-disciplinary team approach to the management of patients.
The allergy team at Royal Brompton is also involved in research to better understand and treat allergies. Professor Durham has just commenced a large new study called the Graduate study, looking at new ways of treating hay fever. Recent food allergy research I have led includes the first UK study on the plant food allergy known as lipid transfer protein allergy, and a novel study demonstrating a link between pollen food syndrome and Irritable Bowel Syndrome.