What Causes Eczema?

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Eczema (atopic dermatitis) is a chronic, recurrent skin disease which commonly occurs in infancy and early childhood but can continue or start in adulthood. Like other allergies and asthma, atopic dermatitis tends to run in families.

It is important to note that atopic dermatitis is not a rash that itches. Rather, it is an itch, that when scratched, results in a rash. Therefore, if the itching can be controlled, and there is no scratching, there will be no rash (eczema).

Atopic dermatitis is very common in childhood, affecting up to 20 percent of kids, usually before the age of 5. The disease is less common in adults, affecting only 1 to 3 percent of the population, although it can start at any age. It is rare to see atopic dermatitis in adults over 50 years of age.

In general, when atopic dermatitis occurs in infants, it usually is more severe—although many cases resolve or improve in later childhood. Children with atopic dermatitis are much more likely to have other allergic diseases, including allergic rhinitis and asthma.

Diagnosis

The diagnosis of atopic dermatitis is made by the history of the symptoms and the examination of the patient by a physician. There is no laboratory test to diagnose this condition. There are three criteria that must be present in order to diagnose atopic dermatitis:

  1. Atopy. Research shows that 30 percent of patients with atopic dermatitis have no family history of atopy. There may be rare cases in which a person has atopic dermatitis without evidence of atopy. Dry skin is a hallmark of atopic dermatitis, partly because the skin barrier function is compromised in atopic dermatitis, increasing trans-epidermal water loss. Also contributing to the dry skin, the natural skin oils in atopic dermatitis may be structurally defective and, thus, less moisturizing.
  1. Pruritis. This is the medical term used for itching. The patient must have itching and scratching in order for the rash to occur. If the skin or areas of the rash do not itch or have not been scratched, then the person does not have atopic dermatitis.
  2. Eczema. This refers to the appearance of the rash in patients with atopic dermatitis and occurs in other skin diseases as well. The rash appears red with small blisters or bumps. These may ooze or flake with further scratching. Over the long term, the skin appears thickened and leathery.

    Location

    The location of eczema is dependent on the area of the body that is scratched. In infants and very young children, this rash involves the face (especially the cheeks), chest and trunk, back of the scalp, and may involve the arms and legs. This distribution reflects where the child is able to scratch, and therefore usually spares the diaper area.

    In older children and adults, the location of the rash changes to classically involve the skin in front of the elbows and behind the knees. Eczema can also involve the face (especially the eyelids) ​and may be limited to the palms of the hands and soles of the feet in certain people.

    Triggers

    Itching of the skin can be caused by irritants, infections, allergies, and stress. Irritants cause itching through direct stimulation of the skin and include harsh soaps, chemicals, wool fabrics, heat, and sweating. Avoidance of these irritants through the use of gentle soaps, wearing cotton clothing, and keeping cool and dry can help prevent itching.

    People with atopic dermatitis are more susceptible to skin infections by various bacterial, fungal, and viral infections. Many have large amounts of a common skin bacterium, called Staphylococcus aureus, which can worsen the itching and eczema.

    Herpes infections (similar to the kind that causes cold sores) and the virus responsible for chicken pox and shingles can also cause severe skin infections in people with atopic dermatitis.

    Allergies can be a significant trigger for itching in people with atopic dermatitis. Usually, allergens that come in direct contact with the skin, such as animal dander and dust mites, cause the most problems, although pollens and mold spores in the air can also worsen the condition.

    Food allergies can also be a major trigger for people with atopic dermatitis, particularly in children. Egg and milk allergies are the most common among children that worsen eczema, although other food allergies are also common.

    Allergy testing is an important part of the evaluation of patients with atopic dermatitis, and avoidance of these triggers, both environmental and food allergens, can significantly improve the disease.

    Sources:

    Atopic Dermatitis Practice Parameters. Ann Allergy Asthma Immunol;93:S1-21.

    Beltrani J. J Allergy Clin Immunol;104:S87-98.

    Sicherer S. J Allergy Clin Immunol;104:S114-22.

    Weston WL. Howe W. Pathogenesis, clinical manifestations, and diagnosis of atopic dermatitis (eczema). In: UpToDate. Corona, R (Ed). UpToDate. 2017.

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