You keep sneezing, your nose runs with thin, watery mucus and your eyes itch, yet the thermometer reads normal and nobody around you is ill. The same trouble comes back every spring, every time you clean the bedroom, or whenever you stroke the neighbour's cat. If that sounds familiar, you are asking exactly the right question: how to recognise an allergy and tell it apart from an ordinary cold. Allergies are no longer a fringe problem — they affect hundreds of millions of people worldwide, and allergic rhinitis alone troubles roughly a quarter of adults in many European countries. This guide walks you through the most common symptoms, shows you how to recognise an allergy to dust mites, pollen, mould, animals and food, and above all, tells you what you can do about it starting today.
Main takeaways if you're short on time
- An allergy is an overreaction of the immune system to normally harmless substances (allergens). The body treats them as a threat and triggers inflammation — hence the runny nose, sneezing, itching and cough.
- The main difference from a cold: with an allergy, the discharge is watery and clear, it comes with itchy eyes and an itchy nose, there is no fever, and the trouble lasts longer than a week or returns in connection with a specific situation.
- The most common allergens are airborne (respiratory): pollen, dust mites, mould spores and animal allergens. These are the hardest to avoid because they are all around us.
- Only an allergist can give you certainty — through skin prick tests or a blood test for specific IgE antibodies. A positive test alone does not mean disease; your symptoms must also match.
- Relief comes from combining three steps: reducing contact with the allergen (barrier bedding, air purifiers, nasal filters), easing the symptoms, and — for suitable patients — treating the cause with allergen immunotherapy.
Disclaimer: This article is for information only and is not a substitute for medical advice. We at nanoSPACE are not doctors. Before starting any treatment, changing medication, or if your symptoms worsen, always consult an allergist, dermatologist or other specialist.
What an allergy is and why it develops
An allergy is a disproportionate — sometimes called hypersensitive — reaction of the immune system to substances our bodies encounter routinely. The difference between an allergic and a non-allergic person is that the allergic person's immune system cannot tolerate these harmless substances and reacts to them, often excessively. Pollen, dust or animal dander do not bother a healthy person, but in someone with an allergy, the body mistakenly judges them to be dangerous and mounts a defence against them.
An allergy develops through a process called sensitisation: with repeated contact, the body gradually becomes hypersensitive to a particular allergen. How long this takes varies enormously — sometimes a few days are enough, while other times it takes years. When the person is then exposed again to the allergen they are sensitive to, immune cells release histamine and other inflammatory substances, and an allergic inflammation of the affected tissue arises. This produces the familiar signs — itchy eyes, a blocked nose, a skin rash. A predisposition to allergies also tends to run in families: if both parents are allergic, the likelihood of their child being allergic rises sharply.
It is worth noting that learning how to recognise an allergy is not the same as pinning down exactly what you are allergic to. Your symptoms will hint that an allergy is the likely culprit and help you recognise an allergy in its typical outlines, but only targeted testing by an allergist will reveal the specific trigger. Before you book that appointment, though, it helps to get your bearings among the typical signs — and that is exactly what the overview below is about.
The most common symptoms of an allergy
Allergic symptoms affect a range of organs and can look very different from one person to the next. Among the most typical are:
- bouts of sneezing and a clear, watery runny nose
- a feeling of a blocked nose even when you are not ill
- an unexplained cough with no preceding respiratory infection
- wheezing and otherwise unexplained difficulty breathing
- itching, burning, watering and red eyes
- itching in the throat, ears or nose
- skin reactions — hives, itchy skin, eczema
- a disproportionate reaction to an insect sting
- nausea, stomach pain or diarrhoea after certain foods
- swollen lips or tongue, or tingling in the mouth
What matters is not only the type of symptom but also its timing and context. If the trouble strikes whenever you are outdoors at a certain time of year, after making the bed, while cleaning, or in the company of a particular animal, that is a strong clue that you are dealing with an allergy. To learn what and when to watch out for, read our guide on the allergy sufferer's calendar from January to December.
How to recognise an allergy and tell it apart from a cold
This is the question almost everyone asks when they want to know how to recognise an allergy before it ruins their whole week: is this a runny nose from a virus, or an allergy? Both begin similarly — the lining of the nose defends itself against something that irritates it. With a cold, it is viruses; with an allergy, it is a specific allergen that triggers the release of histamine. A few clues, however, will reveal the difference fairly reliably.
With a classic cold, which clears up within a week, the nasal secretion gradually becomes thicker and greenish, and a fever, sore throat and body aches often accompany it. With an allergy, by contrast, the runny nose is watery and the discharge is clear, there is no fever, and itching and burning eyes alongside an itchy throat are added to the mix. Duration is decisive: a cold passes in a few days, whereas allergic trouble drags on for weeks or returns predictably in connection with a season or situation. And while you can pass a cold on to someone else, an allergy is not contagious — only you react, and always shortly after contact with the allergen.
Tip: Nasal sprays — which one to choose and what they are for
How to recognise an allergic cough
When you are coughing and are unsure whether a cold or an allergy is to blame, it helps to think through a few points. Duration: a cold usually lasts 7–10 days, whereas an allergic cough can easily go on for several weeks, especially when allergen levels are high. Accompanying symptoms: an allergy comes with itchy, watering eyes and an itchy nose and throat, whereas with a cold, you should expect a fever and a sore throat instead. Patterns over time: an allergic cough gets worse in specific situations — outdoors during pollen season, or at home around an animal; with a dust mite allergy, the cough announces itself mainly at night and in the morning. Response to medication: an allergic cough eases after taking antihistamines, while a viral cough does not respond to them. For a clear diagnosis, however, always see a doctor.
The most common allergens: how to recognise them
The biggest culprits behind allergies are airborne (respiratory) allergens. They cause the most reactions precisely because they are the most widespread — they occur practically everywhere, and because they travel through the air, they are very hard to avoid. Let us look at the main groups in more detail, so you can better identify which allergen is troubling you — because knowing how to recognise an allergy also means working out what sets it off.
Pollen
Plant pollen contains proteins that trigger a reaction in the immune systems of allergy sufferers. Grass pollen is the most common single cause across much of Europe (affecting roughly half of pollen-allergic people), while others react to tree or weed pollen. There are also polyvalent allergies — hypersensitivity to several types of pollen at once. We most often associate a pollen allergy with the pollen season, when it is called hay fever, but bear in mind that depending on the allergen, the trouble can show up almost all year round.
Typical symptoms: a clear, watery runny nose, sneezing, watering and itching eyes, a cough, and skin reactions upon contact with a plant. So you know what and when to watch out for, read the pollen calendar: a guide to allergens from January to December and take a look at what causes a spring pollen allergy.
How to help yourself: follow the pollen forecast and limit time outdoors at the peak, make the most of differences between locations (the city flowers at a different time than the mountains — plan your holiday accordingly), do not dry laundry outside, and rinse your hair when you come home. Leave mowing the lawn to non-allergic family members. Barrier protection for the airways works very well: nasal filters that catch pollen in the nose itself, and barrier nasal sprays that keep the nasal lining clean and moist. Scarves and neck gaiters with a nanomembrane that filter out allergens while remaining breathable are useful too. You will find more detail in How to prepare for allergy season.
Fast relief for the nose and breathing
Dust and dust mites
Dust particles themselves irritate the airways, but they are not allergenic on their own. They become dangerous the moment other allergenic particles cling to them — in the home, most often dust mite droppings and mould. Dust mites live and multiply in bedding, pillowcases and mattresses; a single mattress commonly harbours millions of mites, and after two years of use, a noticeable part of a pillow's weight is the dust in which they live. The mites themselves are not the main problem — the trouble begins when they multiply and produce large amounts of allergenic droppings.
Typical symptoms: a blocked nose, chronic rhinitis, a cough or even asthma, increased morning fatigue, a puffy face, repeated sinus and middle-ear infections, and atopic eczema. A dust mite allergy is a year-round problem, but it gets worse mainly in early autumn, when homes are ventilated less and heated more. There is more in What is dust mite allergy? and in our practical guide on how to get rid of mites in upholstery and mattresses.
How to help yourself: with a dust mite allergy, the primary route is a barrier — keeping mites and their allergens out of the immediate space where you sleep. Reach for anti-dust-mite bedding and barrier mattress covers with a nanofibre membrane that stops mites settling and multiplying. Keep the bedroom cool and dry (below 20 °C, humidity under 50%), vacuum and ventilate regularly, and cut down on high-pile carpets, heavy curtains and upholstered furniture. Air purifiers help as a supplement. The specific procedure for mattresses and upholstery is described in the article on getting rid of mites in upholstery and mattresses.
Mould
For allergy sufferers, filamentous moulds and their reproductive particles — spores — are the unpleasant ones. They are tiny, invisible to the eye and spread much like pollen, except that, unlike pollen, they can also occur indoors and in other interior spaces, mainly where it is damp. Typical symptoms: a runny nose, a cough and asthmatic signs, often harder to read because they are not tied to a specific season.
How to help yourself: ventilate rooms with higher humidity as much as possible — the bathroom, kitchen, pantry and cellar — and tackle the causes of damp so that mould does not form in the first place. Clear away food residues, clean air conditioning units regularly, and consider how to reduce humidity in your home over the long term. Dehumidifiers can help.
Animal allergens
For many people, pets produce very aggressive allergens. You may be surprised to learn that the main allergen is not fur — the coat is merely where allergens concentrate and from which they transfer to us upon contact. The real allergens are mainly in animal saliva, urine, sebum, skin flakes and serum. Among the most aggressive are the allergens of cats and small rodents, and in recent decades, horse allergy has been added to the list too. Typical symptoms: a clear, watery runny nose, a blocked nose, sneezing, watering and itching eyes, swelling, and skin reactions such as hives, itching or eczema. We cover the topic in detail in Allergy to cats, Allergy to dogs and Feather allergy.
How to help yourself: ideally, limit contact with the animal, do not allow it into the bedroom, and vacuum the home regularly. Animal allergens are very light and float in the air for a long time, so a quality air purifier that removes them quickly is highly worthwhile.
Editor's pick
Air purifiers for allergy sufferers
A quiet helper for allergy sufferers and asthmatics. A good purifier captures pollen, animal allergens and fine dust, noticeably improving the air in your bedroom. Before we list a device on our site, we test it ourselves — and we turn down more units than we end up recommending.
View price →Food allergy and cross-reactive allergy
Some allergies do not show up as sneezing, but as trouble after eating: tingling and swelling of the lips or tongue, itching in the mouth, nausea, stomach pain or hives. A peculiar and very common category is cross-reactive allergy, where the immune system confuses similar proteins in pollen and in food. The classic example is the link between birch pollen and raw fruit: up to 70% of people allergic to birch also react to apples, carrots, celery or hazelnuts. Pears, peaches, apricots and cherries can be risky too.
These reactions most often present as oral allergy syndrome — burning or numbness of the lips and the lining of the mouth, or swelling of the tongue, usually within a few minutes of eating the food in question. Cooking often breaks the allergen down, so a baked apple in a strudel may not bother you while a raw one does. We go through how to make sense of this in detail in What is combined (cross-reactive) allergy? A word of caution: unlike mild oral allergy syndrome, a genuine food allergy (for instance to peanuts, tree nuts or shellfish) can be life-threatening — if you experience swelling in the throat, breathlessness or dizziness, call the emergency services.
How an allergy is diagnosed by an allergist
Your symptoms will give you hints, but a reliable answer to the question of how to recognise an allergy — and above all, what exactly you are allergic to — can only come from an allergist. It is worth booking an appointment at the first suspicion; in fact, the first signs are often picked up by a GP, paediatrician, dermatologist or ophthalmologist, who then refers you onwards. Diagnosis rests on two main methods.
Skin prick tests are the most common. Drops of solutions containing selected allergens are placed on the forearm, and each is gently pricked into the upper layer of the skin. If you react to an allergen, an itchy bump forms at the puncture site, which is read after 15–20 minutes. A blood test for specific IgE antibodies from a laboratory is suitable where skin tests cannot be done (for example, with a severe skin condition, or when antihistamines cannot be stopped). It is important to know that a positive test alone does not mean disease — even a healthy person can have positive antibodies or a reaction in the test. It is an allergy only when the positive finding coincides with genuine symptoms after contact with that allergen. That is why the results are always interpreted by a doctor in the context of your own medical history.
Options for managing it: from relief to treating the cause
The good news is that, once you know how to recognise an allergy, you can also live very well with it. An effective approach rests on three pillars and works best when you combine them.
1. Reduce contact with the allergen. This is the most effective and natural step. For mites, rely on barrier bedding; for pollen, on nasal filters and limiting time outdoors at the peak; for animals, on regular cleaning and a clean bedroom; for mould, on tackling damp. Air purifiers help clean the air in the home.
2. Ease the symptoms. Barrier nasal sprays and nasal rinses help against respiratory signs, keeping the nasal lining clean and optimally moist so it defends itself better not only against allergens but also against micro-organisms. For trouble that limits your everyday life, reach for over-the-counter antihistamines; always discuss the choice and suitability with a doctor or pharmacist.
3. Treat the cause. For suitable patients, allergen immunotherapy offers a long-term solution. It works on a similar principle to vaccination: the allergen is administered to the body gradually and regularly in rising doses, so that it learns not to overreact. Treatment usually lasts 3–5 years and is the only approach that acts directly on the cause — studies of pollen immunotherapy show a gradual reduction in symptoms over the successive years of treatment. Whether this route suits you is something an allergist will assess.
Conclusion: listen to your body and don't wait
Learning how to recognise an allergy means noticing patterns — when and where the trouble appears, what sets it off, and whether it disappears when you escape the environment or food in question. A clear, watery runny nose, itchy eyes, a cough without fever, and trouble that lasts longer than a week or returns seasonally are the typical signals. Do not wait for a mild runny nose to turn into a chronic problem or asthma. Take two steps: reduce contact with the most likely allergen (often it is enough to adjust the bedroom and the air you breathe) and book an appointment with an allergist for a firm diagnosis. We are glad to help with the first of these — you will find a complete kit for calmer breathing and better sleep in the For allergy sufferers section.
Frequently asked questions
How to recognise an allergy and tell it apart from a cold?
An allergy gives itself away through a clear, watery runny nose, itching and watering eyes, an itchy throat and the absence of a fever. A cold tends to bring thicker, greenish discharge, a fever and body aches, and it clears up within a week, whereas allergic trouble lasts longer or returns seasonally in connection with a specific situation or allergen.
Can an allergy develop in adulthood?
Yes. An allergy develops through a process of sensitisation that can happen at any age. Sometimes the hypersensitivity builds up over days; at other times, it appears only after years of repeated contact with the allergen. It is not unusual, then, for someone to start reacting to pollen or an animal only as an adult.
Which test reliably reveals an allergy?
An allergist most often uses skin prick tests, where allergens are applied to the forearm and the reaction is read after 15–20 minutes, or a blood test for specific IgE antibodies. A positive result alone does not mean disease, however — it must match your genuine symptoms after contact with the allergen.
What helps most with a dust mite allergy?
The most effective measure is a barrier — keeping mites and their allergens out of the space where you sleep. Anti-dust-mite bedding and barrier covers with a nanofibre membrane help, along with a cooler, drier bedroom (below 20 °C, humidity under 50%), regular cleaning and, as a supplement, an air purifier.
Why do my lips burn after eating an apple when I have hay fever?
This is most likely a cross-reactive allergy, known as oral allergy syndrome. The immune system confuses similar proteins in pollen (typically birch) and in raw fruit or vegetables. The reaction is usually mild and confined to the mouth, and cooking the food often eliminates the problem. With more pronounced swelling or breathlessness, however, see a doctor.
Sources
- American Academy of Allergy, Asthma & Immunology (AAAAI): Allergic conditions and diagnosis. aaaai.org
- NHS: Allergies — overview and diagnosis. nhs.uk
- European Academy of Allergy and Clinical Immunology (EAACI): Allergen immunotherapy. eaaci.org
- Allergy UK: Types of allergy and management. allergyuk.org