Title: Common Allergic Conditions
Key words: hay fever, pollen, perennial allergic rhinitis, allergic conjunctivitis, asthma, leukotrienes, oedema, bronchoconstriction, hypersecretion, peak flow rate, urticaria, nettle rash, itching, angioedema, idiopathic urticaria, skin rashes, dermatitis, prickly heat, insect bite and sting reactions, anaphylactic shock, adrenaline
Date: Sept 2000
Category: 16. Food Intolerance/Allergy
Author: DJE Candlish
Common Allergic Conditions
People who develop allergies may also be described as being atopic. Atopic individuals may develop an allergy to only one allergen or to a range of them. Some eventually 'grow out of’ their allergy. Atopy or allergy is passed on genetically, although some members of a family never develop an allergic condition and one member of a family may develop asthma, another hay fever and another atopic dermatitis. The reasons for this variation are complex and not fully understood. The more common atopic conditions, to be described in more detail here, are:
· hay fever
· atopic eczema (dermatitis)
· skin rashes
· insect bite and sting reactions
Hay fever is the most widespread allergic condition. It affects the nose and sometimes also the eyes. The typical symptoms are sneezing and an itchy, running nose within minutes of breathing in pollen, the major allergen involved. Sometimes the nose becomes blocked due to swelling of the inner lining of the nasal passages. If the eyes are affected, they become red and inflamed and may also be itchy and watery. Intense itching can also be caused by allergens passing in fluid from the nasal cavity to the back of the throat.
These symptoms can last for just a few hours or all day. They can make it difficult to drive, play sports, work or study. School children and students are particularly badly affected, as the hay fever season peaks around the time of summer exams. Hay fever sufferers who are badly affected may also develop asthma symptoms at the peak of the season, as the two conditions are linked.
Hay fever is also known as ‘seasonal allergic rhinitis’ because it mainly occurs between May and August and is at its worst in the pollen season in June and July, when grass and tree pollens are at peak levels. Pollen is the most important allergen involved in hay fever.
The symptoms of hay fever can vary from one person to another, but they are usually directly related to the pollen levels in the air (pollen count). The pollen count is highest in the morning and evening, as the pollen rises high into the atmosphere during the heat of the day. The symptoms may also be aggravated by other environmental factors that can affect the respiratory system. These include cigarette smoke, abrupt temperature changes, perfume, aerosols and air pollution such as car fumes or smog.
People who suffer all year round with nasal symptoms similar to hay fever are said to have ‘perennial allergic rhinitis’. The allergen affecting these people may be mould spores, house dust mites (which live in bedding and soft furnishings feeding on particles shed from human skin), animal dander (particles of fur from household pets) or any other potential allergen which is present all year. People with no nasal symptoms but who have eye symptoms like those of hay fever are said to have allergic conjunctivitis.
How common is hay fever?
At least 12 million people suffer from hay fever in the UK, and this number is increasing every year. Those affected are usually children and young adults although some people aged over thirty also continue to suffer from hay fever. The tendency to hay fever is inherited genetically, and people with both parents affected are unlikely to avoid it. It is also very common for asthma sufferers to have hay fever as well.
How is hay fever diagnosed?
The symptoms and timing of hay fever are usually so obvious that diagnosis is straightforward. Watering eyes and itchy, running nose occurring in early summer are usually due to grass pollen allergy. Response to treatment, often with an anti-histamine, can be used to confirm the diagnosis.
A sufferer's doctor may decide that a specific test to confirm allergy and identify the allergen (skin prick test), is unnecessary.
A family history of hay fever or other allergic conditions also helps to differentiate hay fever from non-allergic conditions like summer colds. Many sufferers never consult a doctor, if their symptoms are mild.
Asthma is less common than allergic rhinitis but is potentially much more serious. The number of people affected by asthma is increasing, just as with hay fever, despite improvements in the treatments available. The typical symptoms include wheezing, cough and breathlessness, but in severe cases, asthma can be fatal. Asthma affects children, adolescents and young adults more than older individuals.
The traditional view of asthma, which was widely held until recently, was that inhaled allergens interacted with IgE and mast cells in the lining of the lungs. This led to the release of inflammatory mediators, such as histamine and leukotrienes, which triggered the inflammatory reaction that causes asthma symptoms.
This reaction involves oedema (swelling) of the mucous membrane lining the airways, broncho-constriction (spasm of the bronchial smooth muscles) and hypersecretion of mucus. The airways of asthmatics that die are often found to be blocked by rubbery plugs of mucus. These factors all cause narrowing of the airways and the breathing difficulties already described. Inflammation also leads to increased sensitivity of the airways to a wide range of inhaled irritants, including cold air, smoke and other pollutants.
Nowadays, it is accepted that although this mechanism accounts for some of the features of acute asthma it does not explain all of the known features of established, chronic asthma. The role of inflammation is now seen as much more important than the allergic component, which is only one of many possible trigger factors. Others include viral infections of the airways and a range of different inflammatory cells and different mediators.
How is asthma diagnosed?
Most asthmatics have a reduced ability to breathe out rapidly and this can be used in diagnosis. A device known as a peak flow meter can be used to measure the maximum rate at which an individual can breathe out (peak flow rate or PFR), before and after treatment with a drug that dilates the airways. If the drug improves the peak flow rate by more than a certain amount, (often >20%) the diagnosis is asthma. There are many other possible diagnostic factors, including family history and symptom pattern but space here is too limited to describe them all.
Urticaria is one of the more common allergic conditions affecting the skin. It is also known as hives and nettle rash (the Latin for stinging nettle is urtica). A nettle sting releases histamine and other irritants into the skin. This causes local inflammation, with dilation of blood vessels and leakage of fluid into the tissues, plus itching and burning sensations.
In someone with urticaria, the affected area tends to be more widespread than in non-atopic individuals, forming intensely itchy, red, raised blotches or wheals over the skin. These tend to appear rapidly and usually disappear within two days or so. They often disappear from one area of the skin only to reappear somewhere else.
These blotches also occur on contact of the skin with an allergen, after taking drugs or certain foods, especially shellfish, or as a reaction to the injection of serum, insect bites or other plant stings. They may also be spontaneous, with no obvious cause. The reaction to food is more generalised than the reaction to localised skin contact.
Urticaria is most common in atopic individuals. In severely affected patients, angioedema can occur. This is a swelling of the lips, eyelids and mucous membranes of the mouth and airways which can be life threatening and requires urgent medical treatment with adrenaline or steroids.
Urticaria is sometimes due to systemic diseases, such as thyroid malfunction, connective tissue disease or lymphoma. It is important to exclude these but the majority of sufferers have chronic idiopathic urticaria. This is a recurrent, relapsing disorder which generally resolves spontaneously.
How is urticaria diagnosed?
The distinctive appearance of the wheals or blotches, coupled with the intense itching, is usually enough for diagnosis of acute urticaria. But, because the skin may be clear again by the time a patient sees their doctor, a detailed history is often necessary. Polaroidâ photographs may be taken if the patient is referred to a skin specialist.
One of the most common of the atopic skin conditions is atopic eczema or dermatitis. Other skin rashes are also very common in atopic individuals, due to the histamine released by allergic reactions. These allergic rashes include prickly heat, which is caused by over exposure to sunlight, heat and other factors, and contact dermatitis, which is an allergic reaction to a substance that comes into contact with the skin. This may be nickel on watches or jewellery, plant materials, the latex in rubber gloves or irritant chemicals encountered at work.
Insect Bites and Stings
Insect bites and stings inject a toxin through the skin. In atopic individuals, the toxin is recognised as ‘foreign’ by the body and an immune response will be generated. In some people, this will only cause a small localised reaction, like urticaria, with some inflammation and itching. In others, the reaction may be more extreme, with a large, painful, inflammation of the skin and the soft tissue underneath it.
In extreme cases, where a person has become sensitised to the toxins in a bee or wasp sting, they may develop anaphylactic shock after a bite or sting. This would require urgent medical help. Adrenaline and corticosteroid treatment may be necessary.
In most cases, however, the bite or sting can be treated without medical help. Any visible sting should be removed carefully, as squeezing a bee sting, in particular, could inject even more toxin into the skin. The affected area should be cleaned with warm water and soap. A cold compress applied directly over the area can relieve some of the discomfort.