Allergies: Causes, Symptoms and Treatment Options

Allergies: Causes, Symptoms and Treatment Options

An allergy happens when your immune system treats a harmless substance, such as pollen, dust mites, a food or a medicine, as a threat. In most common allergies it makes IgE antibodies against that substance, and on later exposure immune cells release histamine and other chemicals that cause sneezing, itching, hives or swelling. Treatment ranges from avoiding triggers and taking antihistamines to immunotherapy that retrains the immune response.

This guide is for anyone who's tired of guessing at their symptoms, wondering whether testing is worth it, or trying to understand options beyond the pharmacy shelf.

Key takeaways

  • Most common allergies (hay fever, food, pet, insect sting) are driven by IgE antibodies and can cause symptoms within minutes.
  • A positive allergy test shows sensitization, not always a true allergy. Results need to be read alongside your history.
  • Steroid nasal sprays are usually the most effective single treatment for hay fever; non-drowsy antihistamines help itch, sneezing and hives.
  • Immunotherapy (shots or under-the-tongue tablets) is the only treatment that changes the underlying allergic response.
  • Anaphylaxis is an emergency. Adrenaline (epinephrine) comes first; antihistamines are not a substitute.

What happens in your body during an allergic reaction?

Think of an allergy as mistaken identity. Your immune system's job is to spot and fight genuine invaders like bacteria and viruses. In allergies, it flags something harmless as dangerous.

The process has two stages:

  1. Sensitization. On early exposure, the immune system makes IgE antibodies specific to the allergen. These attach to mast cells in tissues like the nose, lungs, skin and gut, and to basophils in the blood. You usually notice nothing at this stage.
  2. Reaction. Next time you meet the allergen, it binds to the IgE on those cells. The cells release histamine, leukotrienes, prostaglandins and other chemicals. These widen blood vessels (redness and swelling), increase mucus (runny nose), tighten airway muscles (wheezing) and irritate nerves (itching). This can happen within minutes.

Doctors call this a type I or immediate hypersensitivity reaction. Allergic contact dermatitis, the itchy rash from nickel or fragrance, works differently. It's driven by T cells rather than antibodies, appears a day or two after contact, and is classed as a type IV reaction. That's why it's tested and treated differently.

What are the main types of allergy and their triggers?

TypeCommon triggersTypical symptoms
Allergic rhinitis (hay fever)Tree, grass and weed pollen (seasonal); dust mites, pet dander, mold, cockroaches (year-round)Sneezing, runny or blocked nose, itchy watery eyes
Food allergyMilk, egg, peanut, tree nuts, fish, shellfish, wheat, soy, sesameMouth itching, hives, swelling, vomiting, wheeze; can cause anaphylaxis
Allergic asthmaPollen, dust mites, pets, moldWheeze, cough, chest tightness, breathlessness
Atopic dermatitis (eczema)Irritants, sweat, some allergens, dry airDry, itchy, inflamed skin
Insect venom allergyBee, wasp and hornet stingsLarge local swelling or whole-body reaction
Drug allergyPenicillin and related antibiotics, some othersRash, hives, sometimes severe reactions
Allergic contact dermatitisNickel, fragrance, preservatives, hair dye, latexItchy rash where the substance touched the skin

A small group of foods causes most food allergy reactions. Milk and egg allergies are often outgrown in childhood, while peanut and tree nut allergies more often last for life. Some people with pollen allergy also get tingling in the mouth from certain raw fruits and vegetables, known as oral allergy syndrome, because the food proteins look similar to pollen proteins.

Eczema, food allergy, hay fever and asthma often appear together in the same person, sometimes in sequence through childhood. Doctors call this pattern the atopic march.

Who gets allergies, and why are they more common now?

Allergies run in families. If one or both parents have allergic conditions, a child's chance of developing them is higher. But genes don't explain why allergies have become more common in industrialized countries over recent decades.

The leading explanation began as the hygiene hypothesis: less exposure to microbes in early childhood may leave the immune system poorly calibrated and more likely to overreact. The idea has since shifted toward the microbiome. The bacteria that colonize the gut, skin and airways in early life appear to help teach the immune system tolerance.

Factors linked with higher allergy rates include frequent antibiotic use, less time outdoors, low-fiber diets that change gut bacteria, and air pollution, which can make pollen more allergenic and inflame the airways. On the protective side, growing up on a farm or with dogs has been associated with fewer allergies in many studies. Supporting a diverse gut microbiome with fiber-rich foods is sensible for general health; our guides to easy ways to improve gut health and affordable high-fiber foods have practical ideas, though diet alone won't cure an established allergy.

How are allergies diagnosed?

Diagnosis starts with your story. What symptoms happen, when, where, after what exposure, and what helps? A careful history often points straight to the trigger. Testing then confirms it. The NHS lists skin prick tests, blood tests and supervised food challenges as the main options.

Skin prick testing. A drop of allergen extract is placed on the skin and the surface is lightly pricked. After about 15 to 20 minutes, a raised itchy bump (wheal) with redness suggests sensitization. It's quick and tests many allergens at once, but you need to stop antihistamines beforehand.

Specific IgE blood tests. These measure IgE antibodies to particular allergens. They don't require stopping medication and suit people with widespread eczema or a history of severe reactions.

Supervised food challenge. You eat gradually increasing amounts of the suspected food under medical supervision. It's the most reliable way to confirm or rule out a food allergy, or check whether a child has outgrown one.

Patch testing. Allergens are taped to the back for about two days to diagnose contact dermatitis. It's the right test for rashes from jewelry, cosmetics or work materials, not for hay fever or food allergy.

Here's the catch that trips many people up: a positive skin or blood test means your immune system recognizes the allergen. It doesn't always mean you'll react to it. Plenty of people test positive to foods they eat without trouble. A common mistake is ordering broad food panels without symptoms to guide them, then cutting out safe foods unnecessarily. Testing works best when it's targeted and interpreted by someone experienced.

Drug allergy labels. Penicillin allergy is one of the most commonly recorded allergies, yet many people carrying the label can actually take penicillin safely. The original reaction may have been a viral rash in childhood, a side effect such as nausea, or an allergy that has faded over the years. Being labeled allergic can mean getting broader or less effective antibiotics later. If you have a penicillin allergy on your record but aren't sure what happened, ask your doctor whether you could be assessed. Never test this yourself by taking the drug.

Tests to be wary of. Some clinics and home kits offer IgG food testing, hair analysis or other methods that aren't validated for diagnosing allergy. These often produce long lists of "problem" foods and can lead to restrictive diets with no benefit. Stick to the tests above, ordered for a clear reason.

Which allergy medicines work best?

Medicines treat symptoms; they don't change the underlying allergy. That means they work best taken regularly during your trigger season rather than only when symptoms peak.

Antihistamines. These block histamine at H1 receptors. Older antihistamines such as diphenhydramine and chlorphenamine cross into the brain and cause drowsiness and slowed reactions, so they're a poor choice for daytime use or before driving. Newer, non-drowsy options such as cetirizine, loratadine and fexofenadine are the usual first choice for sneezing, itching and hives.

Steroid nasal sprays. Sprays such as fluticasone, mometasone and budesonide are generally the most effective single treatment for hay fever, and they're better than antihistamines for a blocked nose. They take several days to a couple of weeks of daily use to work fully. Aim the spray slightly outward, away from the middle of the nose, to reduce irritation and nosebleeds.

Leukotriene receptor antagonists. Montelukast can help both hay fever and asthma, but it's usually less effective than a steroid nasal spray for nasal symptoms. In 2020 the FDA added a boxed warning about mood and behavior changes, including suicidal thoughts, so it's generally reserved for people who don't respond to or can't use other options.

Mast cell stabilizers. Cromolyn sodium prevents mast cells from releasing their chemicals. It's very safe but must be used before exposure and several times a day, and it's weaker than steroid sprays. Eye-drop versions are useful for itchy allergic eyes.

Adrenaline (epinephrine) auto-injectors. These are prescribed to people at risk of anaphylaxis. Adrenaline reverses the airway swelling and blood pressure drop of a severe reaction. If you've been prescribed one, carry it at all times, and check the expiry date.

Can immunotherapy cure allergies?

Allergen immunotherapy (also called desensitization) is the only treatment that changes how your immune system responds. It exposes you to gradually increasing doses of the allergen until your body becomes more tolerant. The NHS notes it must be carried out by a medical professional.

Allergy shots (subcutaneous immunotherapy). Injections start with a build-up phase, often weekly for several months, followed by maintenance injections every few weeks for around three to five years. Benefits often last for years after stopping. Shots are used for hay fever, allergic asthma and insect venom allergy, where they offer strong protection against future severe reactions.

Under-the-tongue (sublingual) immunotherapy. Tablets or drops placed under the tongue daily, usually at home after the first dose in clinic. Approved tablets exist for grass pollen, ragweed and house dust mite. They avoid injections, though the effect tends to be somewhat smaller than with shots.

Immunotherapy is a good fit if your symptoms are moderate to severe despite medicines, if you'd like to reduce long-term medication, or if you've had a serious reaction to insect stings. It's a multi-year commitment, so it's worth talking through with an allergist. It isn't used for allergic contact dermatitis.

Oral immunotherapy for peanut allergy is also available in some specialist centers. It aims to raise the amount a child can eat before reacting, to protect against accidental exposure, rather than to let them eat peanuts freely.

What are biologic treatments for allergies?

Biologics are injectable antibody medicines that block specific steps in the allergic pathway. They're expensive and prescribed by specialists, but they've changed outcomes for people with severe disease.

  • Omalizumab binds IgE so less of it can arm mast cells. It's used for severe allergic asthma, chronic hives that don't respond to antihistamines and, more recently, to reduce the risk of reactions from accidental exposure in people with multiple food allergies.
  • Dupilumab blocks IL-4 and IL-13 signaling. It's used for moderate to severe eczema, asthma, chronic sinusitis with nasal polyps and eosinophilic esophagitis.
  • Others such as mepolizumab, benralizumab and tezepelumab (for severe asthma) and tralokinumab and lebrikizumab (for eczema) target different steps.

How do you recognize and treat anaphylaxis?

Anaphylaxis is a severe, whole-body allergic reaction that can become life-threatening within minutes. The NHS lists sudden swelling of the lips, mouth, throat or tongue, difficulty breathing, and fainting or being unable to wake as signs that need an emergency call. Other signs include:

  • A tight throat, hoarse voice or trouble swallowing.
  • Wheezing or noisy, high-pitched breathing.
  • Dizziness, a fast weak pulse or collapse.
  • Often, but not always, hives, flushing, vomiting or stomach cramps.

Skin symptoms aren't always present, so don't wait for a rash to act.

What to do, following NHS guidance:

  1. Use an adrenaline auto-injector straight away if one is available, injecting into the outer thigh.
  2. Call emergency services and say you think it's anaphylaxis.
  3. Lie the person down and raise their legs. If breathing is hard, let them sit up slowly. Don't let them stand or walk, even if they feel better.
  4. If symptoms haven't improved after 5 minutes, use a second auto-injector.
  5. Remove an insect sting if it's still in the skin.

Antihistamines and steroids act too slowly to treat anaphylaxis and should never delay adrenaline. Hospital assessment is needed even if symptoms settle, because a second wave of symptoms can occur hours later. Afterward, ask for an allergy referral, a written emergency plan and two auto-injectors to carry.

Can allergies be prevented?

Food allergy in babies. Advice has reversed in the past decade. Delaying allergenic foods used to be recommended. Then the LEAP trial showed that giving peanut early to high-risk infants sharply reduced peanut allergy compared with avoidance. Guidelines now recommend introducing peanut and other common allergens early, around the time solids start, and keeping them in the diet regularly. Babies with severe eczema or egg allergy may need an allergy assessment first, so check with your child's doctor.

Dust mites. If you're confirmed allergic, use allergen-proof mattress and pillow covers, wash bedding hot each week, keep indoor humidity lower and reduce soft furnishings in the bedroom.

Pollen. Check the pollen forecast, keep windows shut on high-count days, shower and change clothes after time outdoors, and start your nasal spray a couple of weeks before your season begins.

Pets. Keeping pets out of the bedroom and using a HEPA air filter can help a little. Avoidance is most effective, but rehoming a pet is a big decision, and immunotherapy may be an option.

What about skin allergies like eczema, hives and contact rashes?

Eczema. Atopic dermatitis involves a leaky skin barrier, sometimes linked to changes in the filaggrin gene, plus immune overactivity. The weak barrier lets irritants and allergens in, which keeps inflammation going. The foundation of care is daily moisturizing with thick creams or ointments (ceramide-containing products can help), avoiding known irritants, and using prescribed anti-inflammatory creams during flares. Our skincare guide for eczema-prone, sensitive skin covers gentle routines.

Chronic hives. Hives lasting more than six weeks usually have no external trigger. Many cases have an autoimmune element, so avoiding foods rarely helps. Non-drowsy antihistamines are first-line, sometimes at higher than standard doses under a doctor's supervision, with omalizumab as the next step.

Contact dermatitis. This can be allergic or simply irritant (direct damage from soap, solvents or frequent washing). Common allergens include nickel, fragrance, preservatives, latex and hair dye. Patch testing identifies the culprit, and avoidance is the main treatment. If your hands are the problem, our guide to fixing dry, lined hands covers barrier repair.

FAQ

Can you develop allergies as an adult?

Yes. Adults can develop new allergies, including to foods, pollen, pets and medicines, even if they had none as children. Shellfish allergy, for example, often starts in adulthood. If you notice new symptoms after a particular exposure, keep a symptom diary and talk to your doctor about whether testing would help.

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

A food allergy involves the immune system and can cause hives, swelling, breathing problems or anaphylaxis, often within minutes. A food intolerance, such as lactose intolerance, doesn't involve the immune system. It usually causes digestive symptoms like bloating or diarrhea and isn't life-threatening. The difference matters because allergy may require strict avoidance and an emergency plan.

Do allergy shots really work?

For the right person, yes. Allergy shots are well studied for hay fever, allergic asthma and insect venom allergy, and the benefits often last for years after the course ends. They require regular visits over several years and carry a small risk of reactions, so they're given in clinics that can manage those. An allergist can tell you whether you're a good candidate.

When to see a doctor or allergist

Call emergency services for any signs of anaphylaxis. Book an appointment with your doctor if you think you or your child has an allergy, if over-the-counter medicines aren't controlling symptoms, or if you have asthma that isn't well controlled. Ask for an allergist referral after any severe reaction, if you're unsure which foods to avoid, if you want to know whether a childhood allergy has been outgrown, or if you're interested in immunotherapy or biologics.

What to do next

  1. Keep a two-week symptom diary noting time, place, food, pets and pollen forecast.
  2. If hay fever is your main problem, try a daily steroid nasal spray for at least two weeks before judging it.
  3. Ask your pharmacist to swap any drowsy antihistamine for a non-drowsy one if you use it during the day.
  4. If you've ever had a severe reaction, make sure you have an auto-injector, know how to use it and have a written emergency plan.

This article is for general information and is not medical advice. If you think you're having a severe allergic reaction, call emergency services immediately.

Sources

Last reviewed: October 2026.

Comments

Post a Comment

Popular Posts

Muscle Gain Diet: What Actually Works, Kept Simple

Image
To build muscle, most people who lift regularly need about 1.4 to 2.0 grams of protein per kilogram of body weight a day, spread over meals of roughly 20 to 40 grams each, plus enough total food to fuel training. Add consistent strength training and decent sleep, and that covers most of the results. Everything else is fine-tuning. This guide is for anyone who has started lifting and feels buried in conflicting advice about meal timing, shakes and supplement stacks. Here's the short, evidence-based version. Key takeaways The International Society of Sports Nutrition (ISSN) says 1.4 to 2.0 g of protein per kg per day is enough for most exercising people building muscle. Spread protein across the day, about 20 to 40 g per meal, every 3 to 4 hours. Exact timing around your workout matters less than total daily intake. Eating before or after training both work. Creatine monohydrate is the best-supported supplement. Protein powder is a convenience, not a requirement. If you...
Read more

Top 10 Exercises to Help You Sleep Longer and Better

Image
The best exercises for sleep are the ones you'll do most days: brisk walking, yoga, swimming, cycling, strength training and gentle evening stretching all have research linking them to falling asleep faster and sleeping more deeply. Moderate activity can fit almost any time of day. Hard, sweaty workouts are usually best kept away from the last couple of hours before bed. This guide is for you if you lie awake at night, wake up unrefreshed, or want a drug-free way to sleep better, and you'd like to know which kind of movement to try first. Key takeaways Regular activity over weeks matters more than any single workout. Expect gradual change, not an overnight fix. Morning walks outdoors pair movement with daylight, which helps set your body clock. Slow, breath-focused practices such as yoga, tai chi and stretching are the best fit for evenings. Save high-intensity workouts for morning or early afternoon if late sessions keep you up. Exercise helps most sleep problems but...
Read more

Plant-Based Diet for Kidney Disease: Foods, Benefits, Meals

Image
A plant-based diet can suit many people with chronic kidney disease (CKD), and kidney organizations say eating more plants in place of red meat may help slow its progression. The catch is that potassium, phosphorus, protein and sodium still need managing, and your limits depend on your lab results. A renal dietitian should set them. This guide is for people living with CKD, and the family members who cook for them, who want to eat more plants without upsetting their blood work. Key takeaways The National Kidney Foundation says eating more plant-based foods in place of red meat may help prevent and slow the progression of chronic kidney disease. The body absorbs more phosphorus from animal foods than from plant foods, and phosphate additives in processed foods are almost completely absorbed. Foods with 200 mg or more of potassium per serving count as high-potassium, and that includes many fruits, vegetables, beans and nuts. Most adults should keep sodium to no more than 2,300 m...
Read more

Can Pinworms Last for Years? Why Infections Keep Coming Back

Image
No, a single pinworm can't live in your body for years. Adult worms live for only a few weeks. What makes an infection seem to last for months, or even years, is reinfection: eggs get swallowed again and start a new cycle before the old one ends. Break that cycle and the infection clears. This is for parents who've treated a child, seen the itching come back a few weeks later, and started to wonder whether something more serious is going on. Key takeaways Pinworms live for weeks, not years. Long-running "infections" are almost always repeated reinfections. Treatment is two doses of medicine, two weeks apart, because the medicine kills worms but not eggs. Everyone in the household needs treating at the same time, even people with no symptoms. Eggs can survive on bedding, clothes and surfaces for around two to three weeks, so cleaning matters as much as medicine. Pinworm rarely causes serious harm, but see a doctor for babies under 2, during pregnancy, or if t...
Read more

Plant Protein Powder for Acne-Prone Skin: What to Know

Image
If your skin broke out after you started whey protein shakes, switching to a plant-based protein powder is a reasonable experiment. Cow's milk has been linked with acne, and case reports describe acne flares that cleared after whey was stopped. A pea protein powder can support muscle growth, and one trial found results similar to whey. This guide is for people who lift or train and want to keep building muscle without guessing about their skin. It covers what the evidence does and doesn't show, how to choose a powder and how to run a fair test. Key takeaways The milk link is real but not fully explained: the American Academy of Dermatology (AAD) says studies link cow's milk with acne, though the reason isn't clear. Whey evidence is limited: it comes mostly from small case reports and observational studies, not large trials. Pea protein can build muscle: in a 12-week trial, pea and whey produced similar gains in muscle thickness. Sugar matters too: high-gly...
Read more

Soursop Benefits and Risks: Fruit, Leaves and Tea

Image
Soursop fruit is a healthy, fibre-rich tropical fruit that's safe to enjoy in normal amounts. Its leaves and tea have traditional uses with some early lab and animal evidence, but no human trials show soursop treats or cures cancer. High-dose leaf extracts and supplements also raise real concerns about nerve damage, so they deserve caution. This is for anyone who enjoys soursop, has been told to drink the leaf tea for a health problem, or has seen posts claiming it beats chemotherapy and wants a straight answer. Key takeaways The fruit pulp offers fibre, vitamin C and potassium, and fits well in a varied diet. Soursop extracts kill some cancer cells in lab dishes, but that hasn't been shown in people. No reputable cancer organisation supports it as a treatment. Compounds in soursop, especially concentrated in leaves, seeds and bark, can harm nerve cells. Heavy long-term use has been linked to Parkinson-like symptoms. Occasional leaf tea is different from daily concentr...
Read more

Calorie Deficit and Insomnia: Why Dieting Keeps You Awake

Image
Yes, a calorie deficit can cause insomnia. Eating less than you burn lowers overnight blood sugar, raises the hunger hormone ghrelin and nudges cortisol up, and together those signals can wake you at 2 or 3 a.m. The bigger and faster the deficit, the more likely your sleep suffers. This guide is for anyone who started a diet and suddenly sleeps worse. You'll learn how to recognize diet-related sleep trouble, and how to adjust your plan so you keep losing fat without lying awake staring at the ceiling. Key takeaways Diet-related sleep trouble usually looks like waking in the second half of the night, not trouble falling asleep. Large, fast deficits disrupt sleep more than small, steady ones. Keeping protein adequate and saving some carbohydrate for the evening often helps. Poor sleep makes dieting harder: it raises hunger and can shift weight loss away from fat and toward muscle. Loud snoring, gasping, or insomnia that started before the diet needs a medical check, not a ...
Read more

Fruits That Help Reduce Cholesterol and What to Avoid

Image
Avocado, berries, oranges and an apple, fruits that fit a cholesterol-friendly diet Fruits that are rich in soluble fiber, such as apples, pears, oranges, bananas and prunes, can help lower LDL ("bad") cholesterol as part of an overall heart-healthy diet. Avocado can help too when it replaces saturated fat. Fruit alone won't fix high cholesterol, but it's one of the easiest changes to stick with. This guide is for anyone who's just seen a high cholesterol result and wants to know what to put on the plate, and what to watch out for, especially if you take a statin. Key takeaways MedlinePlus lists apples, bananas, oranges, pears and prunes as fruit sources of soluble fiber, which helps lower cholesterol. The suggested target is 10 to 25 grams of soluble fiber a day, from fruit, oats, beans and other foods. In a small controlled study, a moderate-fat diet with one avocado a day lowered LDL more than a similar diet without avocado. Grapefruit, Seville ora...
Read more

No-Sugar Diet: How to Cut Added Sugar Step by Step

Image
A no-sugar diet means cutting added sugars, not the natural sugar in whole fruit, vegetables and plain dairy. You drop soda, sweets and sweetened snacks first, then hunt down hidden sugar in sauces, bread, yogurt and cereal. Most people get through the hardest cravings within one to two weeks. It sounds simple until you start reading labels and find sugar in pasta sauce, salad dressing and "healthy" granola. This guide is for anyone who wants to cut back without a miserable, all-or-nothing approach that collapses by week two. Key takeaways The target is added and free sugars: table sugar, syrups, honey, fruit juice and sweeteners added to processed food. The WHO advises keeping free sugars under 10% of daily calories, with extra benefit below 5%, about 25 grams or 6 teaspoons a day. The CDC reports that US adults average about 17 teaspoons of added sugar a day. Expect cravings, irritability or low energy for the first few days; they usually ease within one to two we...
Read more

Why Am I Losing Muscle Mass? Causes, Signs and Fixes

Image
Most unexplained muscle loss comes from using your muscles less, getting older, or eating too little protein and energy. Less often, it's a sign of nerve damage, a hormone problem or another illness. The good news is that the common causes respond well to regular strength training and enough protein at each meal. Maybe your legs look thinner after a few months at a desk job, or the stairs feel harder than they did last year. This guide is for anyone who has noticed that change and wants to know what's behind it and what to do next. Key takeaways Disuse is the most common cause: muscles shrink when they aren't worked regularly, and this type can often be reversed with exercise and better nutrition. Age plays a part: Cleveland Clinic says age-related muscle loss (sarcopenia) starts in your 30s or 40s and speeds up between ages 65 and 80. Strength training is the main fix: adults should do muscle-strengthening activity on at least 2 days a week, according to the CD...
Read more