What is atopy?
Atopy refers to the genetic predisposition of experiencing an exaggerated immune response to allergens via the overproduction of immunoglobulin E (IgE). The term is derived from the Greek word meaning “the state of being out of place”.
The atopic triad typically consists of atopic dermatitis (skin), asthma (airways), and allergic rhinitis (nasal mucosa). Other atopic conditions include food and drug allergy, allergic conjunctivitis, urticaria, angioedema, and anaphylaxis.
Atopic eczema
Lichenification and hyperpigmentation on the knees in skin of colour due to atopic eczema
Lichenification and hyperpigmentation in atopic eczema on the back of the knees and thighs
Lichenified atopic eczema on the volar wrists
Bilateral redness and lichenification of the lids due to atopic eczema
Click here for more images of atopic dermatitis
Who gets atopy?
The prevalence of atopy is approximately 10–30% in developed countries. Family history is the major risk factor.
Although atopic diseases can occur independently, they often coexist. The progression from atopic dermatitis in infancy to other atopic diseases such as asthma and allergic rhinitis in adulthood is called the ‘atopic march’.
What causes atopy?
While the specific cause is not well understood, a gene-environment interaction is thought to play an important role. Triggers that have been identified include viral respiratory infections, exercise, certain drugs, climatic factors, and psychological factors. Multiple genes with effects on IgE synthesis are also likely involved as well as changes in the skin microbiome potentially affecting skin barrier function.
The pathophysiology of atopy involves mast cell activation which leads to an inflammatory cascade of lipid mediators, cytokines, and histamine.
What are the clinical features of atopy?
Clinical presentation of atopy will vary depending on the specific atopic disease.
Atopic conditions that may present with cutaneous features include:
- Atopic dermatitis (synonymous with eczema) eg, itchy, dry, scaly, thickened skin
- Food and drug allergy
- Allergic conjunctivitis
- Urticaria
- Angioedema
- Anaphylaxis.
Asthma and allergic rhinitis in isolation do not typically present with predominant cutaneous features.
How do clinical features vary in differing types of skin?
There are ethnic variations in patterns of atopic cutaneous diseases. A higher prevalence of atopy is found in developed and industrialised countries. This is explained by socioeconomic status along with environmental and psychosocial factors.
There is some evidence that early infantile exposure to bacteria and protozoa may result in a reduced incidence of atopic disease compared to populations that are brought up in more hygienic conditions (the hygiene hypothesis). Immigrants are more at risk of developing atopy because of exposure to a new set of allergens.
What are the complications of atopy?
Complications of atopy will vary depending on the specific atopic disease. The number of comorbidities and adherence to treatment will influence the risk of potential complications.
For information on atopic dermatitis complications, see complications of atopic dermatitis.
Allergic rhinitis complications
- Sinusitis
- Otitis media
Asthma complications
- Pneumothorax
- Respiratory distress
A severe food allergy with anaphylaxis can lead to life-threatening respiratory distress and is a medical emergency.
How is atopy diagnosed?
Atopy is usually diagnosed clinically and investigations are seldom required.
Investigations that may aid diagnosis include:
- A complete blood cell count (often an eosinophilia)
- Prick testing or scratch testing
- Specific IgE testing (ImmunoCAP specific IgE and RAST tests)
- Allergen provocation tests (occasionally used to identify allergens responsible for allergic asthma and conjunctivitis)
- Pulmonary function testing.
Other investigations could be added depending on the need to explore differential diagnoses, such as:
- Quantitative serum immunoglobulins
- Serum protein electrophoresis
- Stool examination
- Chest X-rays.
It is important to remember that increased IgE is not specific for atopy and total IgE by itself should not be used as a diagnostic tool.
What is the differential diagnosis for atopy?
Since atopy includes multiple diagnoses related to an overactive immune system, there is a long list of differential diagnoses to consider, these include:
- Chronic vasomotor rhinitis
- Pulmonary emphysema
- Allergic or irritant contact dermatitis and other types of eczema
- Lichen simplex chronicus
- Rare diseases associated with increased IgE such as allergic bronchopulmonary aspergillosis, Job syndrome (hyper-IgE syndrome), and IgE myeloma.
What is the treatment for atopy?
General measures
It is often found that control of one atopic condition generally improves the control of the others. General measures include:
- Patient education and counselling
- Avoidance of allergens and irritants such as irritating fabrics or fragrances
- Hydration
- Good hygiene and proper skin care (eg, moisturisers).
Specific measures
Specific measures to treat atopy will depend on the specific atopic condition.
For example, atopic dermatitis treatment may include:
- Moisturisers and emollients
- Topical steroids and topical calcineurin inhibitors
- Antibiotics if secondary bacterial skin infection occurs
- Phototherapy
And in more severe and protracted disease:
- Systemic immunosuppressants such as azathioprine, methotrexate, ciclosporin
- Biological agents such as dupilumab or tralokinumab
- Oral Janus kinase inhibitors.
For more information see treatment of atopic dermatitis.
How do you prevent atopy?
Atopy cannot be prevented since it is genetically determined. However, using the general measures described above can help minimise symptoms and avoid potential complications. Identifying and avoiding specific triggers is also important, where possible.
There is currently insufficient data to support the use of probiotics to prevent allergies and atopic conditions in children.
What is the outcome of atopy?
The prognosis for atopy is generally good, although the vulnerability of the immune system tends to persist lifelong. Ultimately, outcomes depend on the severity of the atopy and adherence to treatment.