What is atopic dermatitis?

Atopic dermatitis (or AD) is a chronic, inflammatory, recurring, non-infectious disease that was labelled as a “skin” condition for a very long time. The major symptom of atopic dermatitis is the severely itchy skin. Fifty years ago, experts worldwide maintained that allergies play an insignificant role in atopic dermatitis and that the main causes of the condition were the dry skin and the psychological state of the patient.3,5  Unfortunately, the same mentality still persists to the present day.

When does atopic dermatitis first occur?

 

Atopic dermatitis typically begins in early childhood. Symptoms develop after the first three months of a baby’s life, sometimes even before that time (between the 4th and the 8th week). Approximately 80% of all patients become ill before reaching the age of 2.5 The condition is a result of genetic and environmental factors and ranges in severity from mild and moderate to severe.12 The number of atopic dermatitis patients has increased dramatically in the last few years, especially in the Western world. This is especially true for children. In years 1939 to 1964, 1.3—3% of children were affected by the condition. Between the years 1980 and 2005, the percentage of the little patients has risen to 20,5,25  according to some sources, even to 30.21  In one third of the children, atopic dermatitis disappears as they reach puberty. The other two thirds have the condition for life or see it recur later, in adulthood.5 After the first onset of symptoms in early childhood, the illness persists for an average of six years.26 However, it can first appear or reappear at any stage in one’s life.  The percentage of adult patients ranges from 3 to 5%.18,26

Atopic dermatitis types

Essentially atopic dermatitis can be divided into two types: the extrinsic (or allergic) type, which affects 80% of the patients, and the intrinsic (or non-allergic) type, which affects 20% of the patients.

  • The extrinsic type involves high levels of serum IgE antibodies and the presence of specific serum IgE antibodies for environmental and food allergens. The course of the illness for patients with the extrinsic type is much more complicated and difficult than for patients with the intrinsic type of atopic dermatitis.
  • The intrinsic type of atopic dermatitis involves normal ranges of serum IgE antibodies and the absence of any specific serum IgE antibodies.9 This type is not yet well researched and it is possible that the patients may have specific serum IgE antibodies for allergens that are yet to be discovered.5,10 The intrinsic type occurs much more often in children (especially girls) than in adults, begins later in life and has a milder course than the extrinsic type.17

Patients of both types can develop eosinophilia.44

Risk factors for developing atopic dermatitis

Risk factors for the development of atopic dermatitis are numerous: mutations in the gene for the production of filaggrin, family history of atopy, having a high education, living in a small family, living in an urban environment (the hygiene hypothesis), drinking alcohol and taking antibiotics during pregnancy, experiencing stress during pregnancy, experiencing stress in general, suffering from obesity, living in certain climates, living in places with high air pollution, etc. 8,19-22,55

Currently, there are two etiological hypotheses for atopic dermatitis that are not mutually exclusive.3,6,8,45

  • The epidermal barrier dysfunction hypothesis (the “from-without” concept): The hypothesis is based on the premise that atopic dermatitis is caused by a dysfunctional skin barrier, which is the result of a low level of lipids in the epidermis and the mutations in the filaggrin production gene. The gene mutation can be found in 15—50% of atopic dermatitis patients. The skin of such patients quickly loses moisture and is therefore dry, sensitive and can be penetrated by allergens and microorganisms, which trigger the immune system response.
  • The immune dysregulation hypothesis (the “from-within” concept): This hypothesis is based on the premise that atopic dermatitis is caused by a dysregulation in the immune system of the patients. The patients’ bodies become more prone to inflammatory responses, which expresses itself as the imbalance in the functioning of Th1 and Th2 lymphocytes. In the acute phase of the illness, the body responds with a heightened level of Th2 cells, which leads to the increased production of serum IgE antibodies and lowers the production of the protein filaggrin.

The course of the illness

Atopic dermatitis in babies

In babies, atopic dermatitis usually develops 3 months after birth, sometimes even between the 4th and the 8th week of the baby’s life.  Approximately 80% of the cases develop before the age of two.5 The inflammation usually appears on the baby’s cheeks, forehead, scalp and behind the ears. The skin changes may spread to the upper body and the extremities. The skin is red and dry, shows signs of scratching and rubbing, and can typically be found “weeping”.  The area where the baby’s skin comes in contact with the diaper is unaffected.12,13

Atopic dermatitis in children

In children between the ages of 2 and 12, atopic dermatitis typically manifests itself as inflammatory hotspots in the bends of the elbows and knee and creases on the palms that can spread to other parts of the body. Skin is damaged in the mouth, eyelid and neck area, with the entire face being affected. The skin is thick, red, dry and scabby with signs of scratching. It can also typically peel off and become weepy.5,12,13

Atopic dermatitis in teenagers and adults

Adult and teenage patients with atopic dermatitis typically experience complications of the condition. Just like in children, the inflammations cover different body parts and can spread from elbow and knee bends and palm creases to the rest of the body. The skin on the neck and the face is heavily affected, and 30% of the patients also develop inflammations all over their palms. The skin thickens, is red, dry and scabby, with scratching marks. It may peel off and become weepy. Frequently, other conditions develop alongside atopic dermatitis, such as asthma, arthritis, inflammatory bowel disease, depression, etc.5,6,12

Accompanying conditions

Patients with atopic dermatitis very frequently also suffer from allergic conjunctivitis (hay fever), asthma and food allergies. The state is known as the atopic triad (atopic dermatitis, hay fever, asthma) or the atopic march (atopic dermatitis, hay fever, asthma, food allergies). Two thirds of the patients with atopic dermatitis develop hay fever and one third (according to some sources even 50%) become affected with asthma. At least a third of the children with atopic dermatitis are found to be allergic to food. According to some sources, as much as 60% child patients show a reaction to the most common food allergens (milk, egg white, wheat flour, soy and peanuts).46,47

The conditions in the atopic triad or the atopic marsh can develop in the opposite order.5,11 When the skin symptoms occur together with other atopic symptoms, we are witnessing a systemic condition that affects different organs.  Given this fact, many experts have found it necessary to extend the narrow definition of atopic dermatitis as a skin disease to the genetically and environmentally caused, systemic and autoimmune disease.3,5,17,29