An allergy is a reaction the body has to a particular food or substance.
Allergies are very common. They're thought to affect more than one in four people in the UK at some point in their lives.
They are particularly common in children. Some allergies go away as a child gets older, although many are lifelong. Adults can develop allergies to things they weren't previously allergic to.
Having an allergy can be a nuisance and affect your everyday activities, but most allergic reactions are mild and can be largely kept under control. Severe reactions can occasionally occur, but these are uncommon.
Substances that cause allergic reactions are called allergens. The more common allergens include:
- grass and tree pollen - an allergy to these is known as hay fever (allergic rhinitis)
- dust mites
- animal dander (tiny flakes of skin or hair)
- food - particularly nuts, fruit, shellfish, eggs and cow's milk
- insect bites and stings
- medication - including ibuprofen, aspirin, and certain antibiotics
- latex - used to make some gloves and condoms
- mould - these can release small particles into the air that you can breathe in
- household chemicals - including those in detergents and hair dyes
Most of these allergens are generally harmless to people who aren't allergic to them.
Symptoms of an allergic reaction
Allergic reactions usually happen quickly within a few minutes of exposure to an allergen.
They can cause:
- a runny or blocked nose
- red, itchy, watery eyes
- wheezing and coughing
- a red, itchy rash
- worsening of asthma or eczema symptoms
Most allergic reactions are mild, but occasionally a severe reaction called anaphylaxis or anaphylactic shock can occur. This is a medical emergency and needs urgent treatment.
Read more about the symptoms of allergies.
Getting help for allergies
See your GP if you think you or your child might have had an allergic reaction to something.
The symptoms of an allergic reaction can also be caused by other conditions. Your GP can help determine whether it's likely you have an allergy.
If your GP thinks you might have a mild allergy, they can offer advice and treatment to help manage the condition.
If your allergy is particularly severe or it's not clear what you're allergic to, your GP may refer you to an allergy specialist for testing and advice about treatment.
Read more about allergy testing.
How to manage an allergy
In many cases, the most effective way of managing an allergy is to avoid the allergen that causes the reaction whenever possible.
For example, if you have a food allergy, you should check a food's ingredients list for allergens before eating it. The Food Standards Agency has more information about food allergen labelling.
There are also several medications available to help control symptoms of allergic reactions, including:
- antihistamines - these can be taken when you notice the symptoms of a reaction, or before being exposed to an allergen to stop a reaction occurring
- decongestants - tablets, capsules, nasal sprays or liquids that can be used as a short-term treatment for a blocked nose
- lotions and creams, such as moisturising creams (emollients) - these can reduce skin redness and itchiness
- steroid medication - sprays, drops, creams, inhalers and tablets that can help reduce redness and swelling caused by an allergic reaction
For some people with very severe allergies, a treatment called immunotherapy may be recommended.
This involves being exposed to the allergen in a controlled way over a number of years, so your body gets used to it and doesn't react to it so severely.
What causes allergies?
Allergies occur when the body's immune system reacts to a particular substance as though it's harmful.
It's not clear why this happens, but most people affected have a family history of allergies or have closely related conditions such as asthma or eczema.
The number of people with allergies is increasing every year. The reasons for this are not understood, but one of the main theories is it's the result of living in a cleaner, germ-free environment, which reduces the number of germs our immune system has to deal with.
It's thought this may cause it to overreact when it comes into contact with harmless substances.
Symptoms of allergies
Symptoms of allergies
Symptoms of an allergic reaction usually develop within a few minutes of being exposed to something you're allergic to, although occasionally they can develop gradually over a few hours.
Although allergic reactions can be a nuisance and hamper your normal activities, most are mild. Very occasionally, a severe reaction called anaphylaxis can occur.
Main allergy symptoms
Common symptoms of an allergic reaction include:
- sneezing and an itchy, runny or blocked nose (allergic rhinitis)
- itchy, red, watering eyes (conjunctivitis)
- wheezing, chest tightness, shortness of breath and a cough
- a raised, itchy, red rash (hives)
- swollen lips, tongue, eyes or face
- tummy pain, feeling sick, vomiting or diarrhoea
- dry, red and cracked skin
The symptoms vary depending on what you're allergic to and how you come into contact with it. For example, you may have a runny nose if exposed to pollen, develop a rash if you have a skin allergy, or feel sick if you eat something you're allergic to.
See your GP if you or your child might have had an allergic reaction to something. They can help determine whether the symptoms are caused by an allergy or another condition. Read more about diagnosing allergies.
Severe allergic reaction (anaphylaxis)
In rare cases, an allergy can lead to a severe allergic reaction, called anaphylaxis or anaphylactic shock, which can be life-threatening.
This affects the whole body and usually develops within minutes of exposure to something you're allergic to.
Signs of anaphylaxis include any of the symptoms above, as well as:
- swelling of the throat and mouth
- difficulty breathing
- blue skin or lips
- collapsing and losing consciousness
Anaphylaxis is a medical emergency that requires immediate treatment. Read more about anaphylaxis for information about what to do if it occurs.
If you think you have an allergy, tell your GP about the symptoms you're having, when they happen, how often they occur and if anything seems to trigger them.
Your GP can offer advice and treatment for mild allergies with a clear cause.
If your allergy is more severe or it's not obvious what you're allergic to, you may be referred for allergy testing at a specialist allergy clinic.
The tests that may be carried out are described below.
Skin prick testing
Skin prick testing is one of the most common allergy tests.
It involves putting a drop of liquid onto your forearm that contains a substance you may be allergic to. The skin under the drop is then gently pricked with a needle. If you are allergic to the substance, an itchy, red bump will appear within 15 minutes.
Skin prick testing is painless and very safe. Make sure you don't take antihistamines before the test, as they can interfere with the results.
Blood tests may be used instead of, or alongside, skin prick tests to help diagnose common allergies.
A sample of your blood is removed and analysed for specific antibodies produced by your immune system in response to an allergen.
Patch tests are used to investigate a type of eczema known as contact dermatitis, which can be caused by your skin being exposed to an allergen.
A small amount of the suspected allergen is added to special metal discs, which are then taped to your skin for 48 hours and monitored for a reaction.
If you have a suspected food allergy, you may be advised to avoid eating a particular food to see if your symptoms improve.
After a few weeks, you may then be asked to eat the food again to check if you have another reaction.
Don't attempt to do this yourself without discussing it with a qualified healthcare professional.
In a few cases, a test called a food challenge may also be used to diagnose a food allergy.
During the test, you're given the food you think you're allergic to in gradually increasing amounts, to see how you react under close supervision.
This test is riskier than other forms of testing, as it could cause a severe reaction, but is the most accurate way to diagnose food allergies. And challenge testing is always carried out in a clinic where a severe reaction can be treated if it does develop.
The treatment for an allergy depends on what you're allergic to. In many cases, your GP will be able to offer advice and treatment.
They'll advise you about taking steps to avoid exposure to the substance you're allergic to, and can recommend medication to control your symptoms.
Avoiding exposure to allergens
The best way to keep your symptoms under control is often to avoid the things you're allergic to, although this isn't always practical.
For example, you may be able to help manage:
- food allergies by being careful about what you eat
- animal allergies by keeping pets outside as much as possible and washing them regularly
- mould allergies by keeping your home dry and well-ventilated, and dealing with any damp and condensation
- hay fever by staying indoors and avoiding grassy areas when the pollen count is high
- dust mite allergies by using allergy-proof duvets and pillows, and fitting wooden floors rather than carpets
Read more about preventing allergic reactions.
Medications for mild allergies are available from pharmacies without a prescription, but always ask your pharmacist or GP for advice before starting any new medicine, as they're not suitable for everyone.
Antihistamines are the main medicines for allergies. They can be used:
- as and when you notice the symptoms of an allergic reaction
- to prevent allergic reactions - for example, you may take them in the morning if you have hay fever and you know the pollen count is high that day
Antihistamines can be taken as tablets, capsules, creams, liquids, eye drops or nasal sprays, depending on which part of your body is affected by your allergy.
Decongestants can be used as a short-term treatment for a blocked nose caused by an allergic reaction.
They can be taken as tablets, capsules, nasal sprays or liquids. Don't use them for more than a week at a time, as using them for long periods can make your symptoms worse.
Lotions and creams
Red and itchy skin caused by an allergic reaction can sometimes be treated with over-the-counter creams and lotions, such as:
- emollients (moisturising creams) to keep the skin moist and protect it from allergens
- calamine lotion to reduce itchiness
- steroids to reduce inflammation (see below)
Steroid medications can help reduce inflammation caused by an allergic reaction. They're available as:
- nasal sprays and eye drops for an inflamed nose and eyes
- creams for eczema and contact dermatitis
- inhalers for asthma
- tablets for hives (urticaria)
Sprays, drops and weak steroid creams are available without a prescription. Stronger creams, inhalers and tablets are available on prescription from your GP.
Immunotherapy may be an option for a small number of people with certain severe and persistent allergies who are unable to control their symptoms using the measures above.
The treatment involves being given occasional small doses of the allergen - either as an injection, or as drops or tablets under the tongue - over the course of several years.
The injection can only be performed in a specialist clinic under the supervision of a doctor, as there is a small risk of a severe reaction. The drops or tablets can usually be taken at home.
The aim of treatment is to help your body get used to the allergen so it doesn't react to it so severely. This won't necessarily cure your allergy, but it will make it milder and mean you can take less medication.
Treating severe allergic reactions (anaphylaxis)
Some people with severe allergies may experience life-threatening reactions, known as anaphylaxis or anaphylactic shock.
If you're at risk of this, you'll be given special injectors containing a medicine called adrenaline to use in an emergency.
If you develop symptoms of anaphylaxis, such as difficulty breathing, you should inject yourself in the outer thigh before seeking emergency medical help.
Read more about the treating anaphylaxis.
The best way to prevent an allergic reaction is to avoid the substance that you're allergic to, although this isn't always easy or practical.
Below is some practical advice that should help you avoid the most common allergens.
House dust mites
One of the biggest causes of allergies are dust mites, which are tiny insects found in household dust. You can limit the number of mites in your home by:
- choosing wood or hard vinyl floor coverings instead of a carpet
- fitting roller blinds that can be easily wiped clean
- choosing leather, plastic or vinyl furniture instead of upholstered furniture
- cleaning cushions, soft toys, curtains and upholstered furniture regularly, either by washing (at a high temperature) or vacuuming
- using tested allergy-proof covers on mattresses, duvets and pillows
- using a vacuum cleaner fitted with a HEPA (high efficiency particulate air) filter, because it can trap more dust mites than ordinary vacuum cleaners
- regularly wiping surfaces with a damp, clean cloth - avoid dry dusting, as this can spread dust into the air
Concentrate your efforts of controlling dust mites in the areas of your home where you spend the most time, such as the bedroom and living room.
You can find more information on allergies in the home on the Allergy UK website.
It's not the pet fur that causes an allergic reaction. Instead, it's flakes of their dead skin, saliva and dried urine.
If you can't permanently remove a pet from the house, you could try:
- keeping pets outside as much as possible, or limiting them to a particular area of the house, preferably an area without carpet
- not allowing pets in bedrooms
- washing pets at least once a week
- regularly grooming pets outside
- regularly washing all bedding and soft furnishings on which a pet has lain
- using an air filter in rooms where you spend most of your time
- increase ventilation with fans, air-conditioning or by opening windows
If you're visiting a friend or relative with a pet, ask them not to dust or vacuum on the day you're visiting, as this will stir up the allergens into the air. Taking an antihistamine medicine about an hour before entering a pet-inhabited house can also help reduce your symptoms.
The Allergy UK website has more information about domestic pet allergies.
Tiny particles released by moulds can cause an allergic reaction in some people.
You can help prevent this by:
- keeping your home dry and well-ventilated
- removing any indoor pot plants from your home
- not drying clothes indoors, store clothes in damp cupboards or packing clothes too tightly in wardrobes
- dealing with any damp and condensation in your home
- avoiding damp buildings, damp woods and rotten leaves, cut grass and compost heaps
By law, food manufacturers must clearly label any foods that contain something that's known to cause allergic reactions in some people. By carefully checking the label for the list of ingredients, you should be able to avoid an allergic reaction.
People with food allergies most often experience an allergic reaction while eating out at a restaurant. You can avoid this by:
- not relying on the menu description alone (remember, many sauces or dressings could contain allergens)
- communicating clearly with the waiting staff and asking for their advice
- avoiding places where there's a chance that different types of food could come into contact with each other, such as buffets or bakeries
- let restaurant staff you know your dietary requirements, including how severe your food allergy or intolerance is
- always check what allergens are in the dish even if you have eaten it before, as recipes and ingredients can change
Remember, simple dishes are less likely to contain "hidden" ingredients. If you're not sure about a dish, don't risk it
Pollen allergies - more commonly known as hay fever - are caused when trees and grasses release pollen into the air. Doctors often call hay fever allergic rhinitis.
Different plants pollinate at different times of the year, so the months that you get hay fever will depend on what sort of pollen(s) you are allergic to. Typically, people are affected during spring (trees) and summer (grasses).
To help keep your hay fever under control, you can:
- check weather reports for the pollen count and stay indoors when it's high, if possible
- avoid drying clothes and bedding outside when the pollen count is high
- wear wraparound sunglasses to protect your eyes
- keep doors and windows shut when possible
- shower and change your clothes after being outside
- avoid grassy areas, such as parks and fields - particularly in the early morning, evening or night, when the pollen count is highest
- if you have a lawn, try asking someone else to cut the grass for you
Read more about preventing hay fever.
Insect bites and stings
If you've ever suffered a bad reaction to an insect bite or sting, it's important to take precautions to minimise your risk.
When you're outdoors, particularly in the summer, you could:
- cover exposed skin
- wear shoes
- apply insect repellent
- avoid wearing strong perfumes or fragrances, as these can attract insects
Read more about preventing insect bites and stings.
Preventing severe allergies (anaphylaxis)
If you're at risk of experiencing a severe allergic reaction (anaphylaxis), make sure you carry two adrenaline auto-injectors with you everywhere.
Wearing a MedicAlert or Medi-Tag medallion or bracelet can make others aware of your allergy in an emergency.
Consider telling your teachers, work colleagues and friends, so they can give you your adrenaline injection in an emergency, while waiting for an ambulance.
Read more about preventing anaphylaxis.