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An allergen is any substance that causes an allergic reaction2. It could be something you touch or a food or medicine you ingest1. Most allergies are atopic, meaning they’re caused by what is known as Type 1 hypersensitivity2. Atopic disorders are very common and often run in families2.


Urticaria and angioedema

Urticaria is also called hives1. It’s a common skin condition that typically presents as itchy, raised wheals that could be anything from a few millimetres to several centimetres in size3.

The itchiness can interfere with daily life and disrupt sleep. Usually, it’s not serious and disappears on its own, but it can be a symptom of anaphylaxis or, rarely, of an underlying condition3. Urticaria can also be chronic, coming and going3. It’s considered chronic if it lasts more than six weeks3.

Angioedema is a type of urticaria where the swelling involves deeper tissues below the skin1. It can affect any part of the body, but most commonly affects the genitals, eyelids and lips1. It can be fatal when the throat is involved4.

Atopic dermatitis

Atopic dermatitis (AD), also known as atopic eczema, is a chronic skin disease that comes and goes in flares5.

It’s often associated with other allergic conditions, such as food allergies, allergic rhinitis and asthma5. AD is the most common skin disease in children5. It affects 15 – 20% of children and 1 – 3% of adults worldwide5. It has a big impact on overall quality of life, socially, at school and at work5.

Allergic contact dermatitis

Contact dermatitis is inflammation of the skin caused by touching a substance6.

In most cases, the substance is an irritant, which damages the skin and causes the reaction6. This is called irritant contact dermatitis and can be prevented by avoiding contact with irritants, e.g., by wearing gloves6.

Allergic contact dermatitis is when an immune response is triggered by your skin touching an allergen6. It is one of the most common work-related conditions7. It can develop after exposing the skin to something new or something that’s been used for months or years, as weak allergens can take months to start causing dermatitis6. It affects quality of life and can lead to long periods of sick leave7.

Other allergic skin conditions1

Hand dermatitis: An inflammatory skin disease that mostly only affects the hands. Working with chemicals, epoxy glues and rubber can increase the chance of developing hand dermatitis.

Photo allergic reaction: When a medication taken either orally or applied to the skin is altered by UV rays from the sun, prompting an immune system response. It is rare.

Phototoxic reaction: When something you take or a substance you touch (e.g., a plant) makes your skin sensitive to UVA radiation from the sun, causing a sunburn-like reaction. 

Clinical presentation

The clinical features of urticaria and angioedema are as follows:

  • Urticaria can appear anywhere on the skin3.
  • Urticaria lesions are itchy and can be round, elongated or have different shapes3.
  • Angioedema mostly occurs in the face, lips, mouth, upper airways, genitals, and extremities3.
  • Angioedema is not itchy1.
  • Both come on quickly, within minutes to hours of exposure to the allergen1.

Clinical presentation of atopic dermatitis:

  • There are typically three phases5:
  • Acute AD consists of weeping blisters that form a crust when they burst.
  • Subacute AD consists of dry, scaly red lesions and plaques.
  • In chronic AD, the skin is thickened and leathery from scratching.
  • Itching is the main feature of AD and the one that people find most impacts their quality of life5.
  • In babies, AD may cover the whole body1. In crawling children, AD mainly occurs on the front of the knees and back of the elbows1. In older children, AD commonly develops on the back of the knees, front of the elbows and wrists1. In adults, it occurs on the same areas as older children, as well as the front and side of the neck, eyelids, forehead, wrists, tops of the feet and hands5.

Clinical presentation of allergic contact dermatitis:

  • Intense itching6.
  • Red, raised rash6.
  • Blistering, weeping and swelling may occur1.
  • In chronic cases, thick, scaly plaques can develop1.
  • Rash is usually on the skin that came into contact with the allergen, but it can be spread to other areas by the person’s hands6.
  • Typically occurs within 12 – 48 hours of exposure, but it can take up to two weeks6.
  • In rare cases, it may last for months or years6.


There are many causes for urticaria3. Common causes include:

  • Certain foods, such as fish, shellfish, nuts, beans and spices1.
  • Some medicines, such as penicillins, cephalosporines, tetracyclines and sulphonamides1.
  • Insect venom3.
  • Infections (the leading cause in children)3.
  • Physical stimuli, including pressure, cold, heat, and raising the core temperature3.
  • In rare cases, systemic diseases, such as Hashimoto thyroiditis, mastocytosis, systemic lupus erythematosus, Sjögren’s syndrome, rheumatoid arthritis, vasculitis, coeliac disease, and lymphoma3.

Triggers for atopic dermatitis:

  • Staphylococcus aureus infections on the skin1
  • Viral infections5
  • Food allergies5
  • Perfumes and cosmetics5
  • Weather: Extremes of hot or cold can cause sweating or dry skin that leads to itching5.
  • Wool (for children)5
  • Environmental allergens, such as dust mites, mould, pollen, cigarette smoke and pet hair can make symptoms worse5.

Common allergens that trigger allergic contact dermatitis6:

  • Plants that contain the oil urushiol, such as poison ivy, poison oak, poison sumac, gingko fruit and mango skin
  • Nickel in jewellery
  • Perfumes and make-up
  • Components of rubber
  • Nail polish
  • Chemicals in shoes
  • Certain medications, including hydrocortisone cream and antibiotic creams
  • Laundry detergents (uncommon).


The healthcare provider will do a clinical examination3. This includesa thorough physical exam, as well as a very detailed history, including3:

  • When it started
  • Timing
  • Location and severity of symptoms
  • Potential triggers
  • Family history
  • Allergies
  • Recent travel
  • Recent illnesses
  • Sexual history
  • Drug use
  • Other, non-skin-related symptoms in order to rule out anaphylaxis.

Diagnosing atopic dermatitis

Your healthcare provider will take a detailed history and do a physical examination, which will focus on the appearance of the skin lesions5.  

In babies and young children, diagnosing atopic dermatitis is usually straightforward, but in adults it can be trickier8. There is a strict list of diagnostic criteria that your healthcare provider will use to rule out other, similar skin conditions and confirm a diagnosis of AD5. Itching is an essential feature in diagnosing AD5.

Diagnosing allergic contact dermatitis

Your healthcare provider will take a detailed history and do a physical examination6. Eliminating the suspected allergen to see if symptoms improve is a way to test the diagnosis6.

In some cases, your healthcare provider may refer you to an allergist or dermatologist for patch testing6. A small amount of the suspected allergen is applied to a patch of clean, dry skin (usually the inside of the forearm) and covered with adhesive tape; if a reaction develops, this indicates an allergy to the substance1.


Urticaria and angioedema

Urticarial lesions usually clear up on their own within 24 hours, although new wheals may develop3. Angioedema may take a few days to clear up3. The most important aspect of treatment is avoidance of identified triggers3. Using aspirin, NSAIDs, alcohol and wearing tight clothing can make symptoms worse and should be avoided3. Chronic urticaria is usually managed with daily antihistamines, but other options may be considered if it is not under control3.

Atopic dermatitis

Treatment is multifaceted and requires a stepwise approach based on the severity of the AD8. The main goal of treatment is to prevent the itch, as scratching the skin makes AD worse5. In severe cases that don’t respond to treatment, your healthcare provider may refer you to an allergist or dermatologist8.

Allergic contact dermatitis

Usually clears up on its own 2 – 4 weeks after eliminating contact with the allergen6. In the meantime, the focus can be on treating the symptoms6.

Medication options

Urticaria and angioedema3:

  • Antihistamines are the first line of treatment.
  • Corticosteroids in severe cases, especially for angioedema and flare-ups of chronic urticaria.
  • Epinephrine auto-injections if there is a risk of anaphylaxis or angioedema that threatens the airways.

Atopic dermatitis8:

  • Mild cases: Low- to mid-potency steroid creams or ointments as needed.
  • Moderate to severe cases: Mid-potency steroid cream or ointment regularly. Alternatives are topical calcineurin inhibitors (e.g., tacrolimus) and crisaborole.
  • Topical anti-inflammatories can be used once or twice a week proactively or once or twice a day during flares.
  • Dupilumab or systemic immunosuppressants if the AD is severe and doesn’t respond to treatment.

Other treatment alternatives for severe atopic dermatitis include8:

  • Phototherapy
  • Cyclosporine
  • Methotrexate
  • Azathioprine
  • Mycophenolate mofetil.

Allergic contact dermatitis:

  • Soothing lotions, such as calamine lotion6 
  • Oat baths6
  • Wet or damp dressings6
  • Topical steroid creams and ointments6
  • Oral steroids in severe cases6
  • Phototherapy in chronic cases7.

Topical antihistamines should be avoided as they can cause contact dermatitis6.


Urticaria and angioedema are best prevented by3:

  • Avoiding triggers.

Atopic dermatitis8:

  • Daily showers or baths
  • Applying emollients and moisturisers to the skin directly after bathing or showering
  • Avoiding triggers, such as irritants, allergens and extreme heat, cold or humidity.

Allergic contact dermatitis is best prevented by7:

  • Avoiding contact with known allergens
  • Wearing protective gear (e.g., gloves or masks) where contact is unavoidable
  • Using barrier creams.

Helpful tools

Allergies are divided into immediate type and delayed type, which take longer to build up9.

There are two tests for immediate type allergies9:

  • Skin prick test: Performed by placing a drop of allergen on the skin, pricking the skin, then wiping the drop away. After 15 minutes, if a hive or bump forms, that indicates an allergy. The larger the reaction, the more likely it’s a true allergy and not just a sensitisation.
  • ImmunoCAP®: A blood test that requires you to have blood taken. It shows allergy as well as sensitisation – the potential to develop an allergy to a substance.

Testing for delayed type reactions can be performed via blood tests and skin patch testing9.

Challenge tests9:

  • Are when a person is given small amounts of a potential allergen in a controlled medical setting, with the amounts increasing every 15 minutes to see if they react (immediate type reaction).
  • They are used for foods and medicines.

If a delayed type allergy is suspected, the suspected allergen is first removed for a few weeks. If symptoms disappear during this time, the suspected allergen is reintroduced to see if symptoms come back.