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Allergies: what you need to know

From hay fever to nut allergy, find out why allergies are on the rise, common triggers and how to manage your symptoms in this complete guide

Written by Helen Foster on January 22, 2019
Reviewed by Prof Michael Rudenko on January 30, 2019

We’ve all heard of allergies – after all, 21 million adults in the UK suffer from at least one¹ – be it merely annoying ones like hay fever, or potentially serious problems like peanut allergy. But do you know what’s really happening to your body when allergy strikes? This guide will give you all the info you need.

What is an allergy?

It’s an abnormal reaction by your immune system to what should really be a normally harmless substance entering your body, like pollen, dust or a food: your body thinks it’s an invader and triggers a reaction designed to protect the body. This means mast cells, which are a type of cell in the immune system, release a substance called histamine – irritating the body. It’s this that triggers allergy symptoms.²

What are common symptoms of allergies?

Symptoms differ depending on the allergy involved, but can include:^3,4

Food allergy:

tingling mouth
swelling of the face, throat, mouth or lips
hives
anaphylaxis

Allergic asthma:

wheezing
trouble breathing
chest tightness
coughing

Atopic dermatitis (eczema):

itchy, red rash
flaky skin

Hay fever:

sneezing
itchy and watery eyes
runny nose

For many, allergy symptoms only affect the body directly exposed to the allergen – for example inhaled allergens like pollen or dust tend to cause problems in the lungs, nose and mouth. Contact allergies to chemicals in washing powder, cosmetic products and to metals found in jewellery, for example nickel, are likely to only affect the skin and have a different, delayed mechanism.

But there is also a very severe reaction to allergens known as anaphylaxis. This can affect many areas of the body at once, and can be life-threatening.⁵

Can anything trigger an allergy?

Theoretically, yes – and you can also develop an allergy to something you’ve eaten or used many times in the past with no problems. However, some substances are more commonly associated with allergy than others, including:

Food: 6-8% of the UK population have a food allergy and the most common edible triggers are nuts, dairy, eggs, shellfish and fruit⁶

Insect bites and stings: 1 in 150 children in the UK are allergic to wasps, and so are 3 in 100 adults⁷

Pollen: One in five people have hay fever in the UK. The main trigger is grass pollen⁸

Other common allergens include:^9,10

dust mites
moulds
latex – found in items like rubber gloves or condoms
medicines, such as ibuprofen and some antibiotics

Ask your GP for an allergy test if you’re not sure what is triggering your allergic reaction.

Who is most at risk of having an allergy?

Allergies are more common in children than adults. You’re also more likely to develop an allergy if someone else in your family has one. A 2014 US report found that more than 100 genes involved in creating an allergic reaction have been identified so far so it’s likely these are passed between family members.¹¹

Are allergies on the increase?

It seems so – cases of food allergy have doubled in the last decade and hospital admissions for severe allergy have increased seven-fold.¹²

Why is this happening? No-one knows. It used to be thought that our clean lifestyles weren’t testing the immune system enough and it was overreacting accordingly, but that idea – known as ‘the hygiene hypothesis’ – is now largely discredited. The latest theory is called ‘old friends hypothesis’ and it suggests that our modern lifestyles are eliminating the type of bacteria in the body that are essential for the proper functioning of the immune system.¹³

The theory hasn’t been proven yet – but there are some studies backing it up. For example, a 2012 study in The Journal of Allergy & Clinical Immunology found that the more children used products containing an antibacterial ingredient called triclosan – found in soaps and toothpaste – the greater their risk of food allergy.¹⁴

What’s the difference between a food allergy and food intolerance?

The main differences are:^15,16

unlike an allergy, an intolerance is usually caused by an absence or decreased activity of a type of enzyme that breaks down food
allergic reactions are fast – usually within minutes, or hours, of being exposed to your trigger. Intolerances can take up to a few days to cause a reaction
allergic reactions can be life-threatening, but this isn’t normally the case for an intolerance
symptoms of intolerance are different from allergies, for example migraine, fatigue, eczema, joint pain and gut health issues, like bloating or irritable bowel syndrome

How to manage allergies

The best way to manage an allergy is to avoid the substance to which you have the reaction.

For allergies where avoidance is harder, like hay fever, antihistamines can prevent your body from releasing histamine in the first place.

However, a number of natural remedies may also play a role in calming the immune system response:

omega-3 – a 2015 Japanese study found it can relieve inflammation in airways for allergic asthma¹⁷
quercetin – this flavonoid found in citrus fruit has been shown to have an anti-inflammatory effect for eczema¹⁸