How common are allergies?
Allergies are increasing across the globe. It’s now estimated that, in some countries, approximately 25% of people suffer from some form of allergy. Types of allergies include allergic rhinitis (hay fever or “sinus”), allergic asthma, food allergy, and allergic skin reactions such as eczema.
In general, allergies are more common in richer countries, and in more affluent individuals within a country.
The reasons for this aren’t well understood, but there are two hypotheses:
• Firstly, people who are more affluent may be exposed to certain factors in their environment that promote allergies in themselves as well as their offspring. Examples include junk food and sugary drinks.
• Secondly, more affluent people might be “missing” certain factors in their environment that are protective – for example, the good germs that people who live in rural areas encounter every day.
Whatever the cause, it’s clear that something serious is happening to humans across the globe: we’re becoming more allergic over time and we seem to be unable to tolerate our own environments.
In South Africa, we have good data on how common certain types of allergic conditions are, and almost no data on others.
For example, we know that:
• About 10–20% of South African children suffer from asthma.
• Allergic rhinitis is even more common at about 30–40%.
• Asthma and allergic rhinitis are both more common in urban than in rural areas.
• Even though asthma and allergic rhinitis are more common in more affluent people, they’re likely to be more severe and less well treated in poorer communities. Essential medications simply aren’t always available.
• The most common triggers for allergic asthma and rhinitis symptoms are house dust mites (especially in the coastal regions) and grass pollens. Other common allergens include cats, dogs, cockroaches, weeds and moulds.
Worldwide, eczema – an allergic disease – occurs in approximately 15–20% of children. It peaks at about two to three years of age and tends to become less common as children grow older.
Most children with eczema either outgrow it, or the eczema becomes more manageable and less severe over time. Eczema medications are commonly available, even in primary-care clinics, but aren’t always given in the quantities needed to treat eczema properly.
Although, at some stage in their lives 20–30% of people believe they have a food allergy, global statistics show that most people who believe this simply aren’t allergic to the suspected food culprits. Worldwide, the true prevalence of food allergy is only about 2–5%.
Food allergy tends to be more common in children than in adults, with the highest prevalence occurring between the ages of one and a half and three years. Many children outgrow their food allergies by the age of five.
In South Africa, the only good data comes from the South African Food sensitisation and Food Allergy (SAFFA) study, which was done in very young children aged one to three. This study showed that 2.5% of urban children in Cape Town have a food allergy. The most common allergen is egg, followed by peanut, milk and fish.
In general, children outgrow milk allergy by three years of age, while peanut, fish and shellfish allergies are more common later in childhood. So, it’s possible that the researchers underestimated the prevalence of these allergies (the study was only done in very young children).
The researchers also proved that food allergy is much less common in rural areas. They looked at children of the same age in rural Eastern Cape and found that only 0.5% of children had a food allergy. They were all allergic to egg, and their allergies were much less severe than in the urban children.
Worldwide, adverse drug reactions (e.g. a reaction to penicillin) affect about 10% of the population.
However, many people who think that they’re allergic to penicillin actually aren’t. Instead, they may have experienced a common side effect of the medication (such as a rash) at some point in their lives. Alternatively, the illness that was treated with the antibiotic may have caused the rash.
It’s therefore important to have suspected allergies investigated by a doctor with skill and an interest in allergy diagnosis and management. You may not be allergic to a particular substance after all.
Reviewed by Prof Mike Levin, Head of Division of Asthma and Allergy at the University of Cape Town:MBChB; FCPaed; MMed; PhD Diploma Allergology; EAACI UEMS Exam in Allergy, FAAAAI, FACAAI. March 2018
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