Allergy Information

An allergic reaction is a term given to the body’s response to exposure of an allergen by skin contact, inhalation, ingestion and in the case of certain drugs or insect venom; injection into the skin. Previous exposure to the allergen may have sensitised the immune system to the substance. This, in itself, does not produce allergy symptoms but ensures that the immune system is ready to produce a reactionary response next time exposure occurs. A non-allergic person will not have a reaction to an allergen. An allergic reaction is caused by an ‘over-reaction’ of the immune system to a substance (the allergen) which in itself is normally considered harmless.

The modern concept of allergy was first introduced into medicine by the Austrian paediatrician Clemens von Pirquet in 1906, although allergic diseases like asthma and eczema have been described by physicians throughout the course of human history. Allergy should be distinguished from atopy, which is a tendency to produce a specific immune molecule called Immunoglobulin E (IgE) in response to exposure to common allergens (something that can be readily demonstrated in a laboratory test). Although there is a strong link between atopy and allergic disease, not everyone with atopy develops an allergy. Similarly, there are some patients with symptoms that are compatible with allergic disease, yet who do not produce IgE on exposure to allergens. Allergy is also not necessarily the same as sensitivity or intolerance to a substance. This is particularly so in the area of food where, for instance, lactose intolerance is not classed as a food allergy because the symptoms do not come from the immune system.

The following key risk factors have been identified:

Genetics: If both parents are allergic, the hereditary risk of allergy in a child is 75%. If only one parent is allergic, the risk is 50%. The risk amongst the rest of the general population is around 10-20%.

Age, sex, and position in the family: Children are, on the whole, more likely to suffer from allergy than adults (there is a tendency to ‘grow out of’ allergic disease, although it can also develop for the first time in an adult). More boys than girls have atopic asthma and hay fever, although this difference between the sexes tends to level out in adult life. Children from large families and those with older siblings are less likely to develop allergies (this could be because they are more exposed to childhood infection, which makes the developing immune system less likely to over-react to an allergen).

Early-life, or extreme/sudden, allergen exposure: some evidence suggests that exposure to allergens like cigarette smoke, traffic pollution, dust, pollen, mould and pet dander in early life may increase a child\'s risk of developing an allergy. For example, breastfeeding for six months or more, instead of bottle feeding, has been shown to decrease the risk of asthma and other allergies in babies. Furthermore, it is worth noting that premature babies are also more at risk of developing allergies than full-term babies.

Case Study
In 1994 the UK suffered what was probably the world’s worst asthma epidemic with hospitals across the country being overwhelmed with admissions. Many feared there had been a leak of poison gas, but some experts now believe that the severe thunderstorms of June that year had produced an unusually high level of tiny particles of pollen in the air, which had triggered asthma attacks in susceptible people (including many who usually suffered only from hay fever).

Asthma: Asthma is the reversible narrowing and hyper-responsiveness (‘twitchiness’) of the, in response to allergen exposure and produces symptoms of wheezing, coughing, chest tightness and breathing difficulty finding, it harder to breathe in than breath out. Asthma attacks are caused by triggers which are either allergens (like house dust mite, mould, pet dander) or irritants like cigarette smoke, traffic pollution or cold air. Asthma is potentially the most serious of allergic diseases. In the UK, during 2008-9, there were nearly 80,000 hospital admissions for asthma of which nearly half were of children aged 14 and under. On average there are 1,500 deaths from asthma in the UK. In 2010, 1,143 people died from asthma, 16 were children aged 14 and under (figures from Asthma UK).

Hay fever (seasonal rhinitis): Hay fever is characterised by itchy nose and eyes, sneezing and runny nose. In the UK it is mainly caused by exposure to grass pollen (perennial rye and timothy grass). To learn more about Hay fever visit our Hay fever information page.

Perennial rhinitis: Rhinitis that persists all year round is known as perennial rhinitis. Sometimes people with perennial rhinitis do experience worse symptoms in the pollen season. Around 50% of those with perennial rhinitis have an allergy while the rest have some other problem with their nose or sinuses. To learn more about Perennial rhinitis visit our Rhinitis information page.

Eczema: The word eczema means ‘boiling’ and refers to the inflammatory rash that appears on the skin. The condition itself is often known as atopic eczema and is caused by an allergy. The word dermatitis, often used interchangeably with eczema, refers to any skin inflammation, allergic or not. To learn more about hay fever visit our Eczema information page.

Urticaria: Also known as nettle rash (from the Latin word ‘urtica’ for nettle), Urticaria shows up as small, itchy swellings or larger red patches on the skin. Allergens like bee and wasp stings, certain foods and drugs may cause Urticaria, but there are also non-allergic causes.

Food allergy: A number of allergic disorders can be triggered by food and so food allergy is not really a disease in its own right. Food allergy, which involves the IgE pathway of the immune system, is not the same as a food sensitivity or food intolerance. The former is a term that has come to describe any adverse reaction to food, including allergy, while food intolerance describes any adverse reaction to food not caused by an allergic mechanism. A pivotal danger of food allergies can be anaphylaxis, which causes swelling of the oesophageal glands and can result in death.

Bee or wasp sting allergy: An allergy to the venom of a bee or wasp sting can cause redness, swelling, and pain at the site. Bee or wasp venom is the second most common cause of anaphylaxis, a severe and potentially fatal allergic reaction involving the whole body.

Allergy to drugs: An allergy to a drug can cause anaphylaxis urticaria and angioedema (otherwise known as hives). These are conditions involving rashes and swelling beneath the skin resulting in noticeable puffiness of the face and throat.

The most common allergens in the UK are inhaled allergens, in the following order:

1. House dust mite
2. Grass pollen
3. Cat Dander
4. Tree pollen

Common food allergens include shellfish, peanuts, tree nuts, strawberries, cow’s milk and eggs. Mould spores, insect venoms, latex and a number of chemicals and drugs are also significant allergens. Also be aware of allergy triggers such as:

- Traffic pollution
- Certain chemicals and gases
- Cigarette smoke

If you are allergic to pollen, you will need to be aware of seasonal variations. Other allergens like house dust mite and traffic pollution, tend to be present year-round. The pollen season varies for different plants and, put simply, it lasts from early Spring to late Autumn. With the continuing trend of global warming, it may be that our pollen season will get longer and longer.

Roughly 30% of the UK population is affected by an allergy at some point in their lives. The UK has the highest allergy rate in Europe and the amount of people diagnosed with an allergy increases every year. There is no clear explanation for this; however, there are two main theories. The first theory is that awareness and diagnosis have improved in recent years. The second theory is that the increase in general air pollution and indoor air pollution have made allergens more common, resulting in more frequent exposure.