By Gay Wardle

Atopic dermatitis is one of the most common and burdensome skin disorders in the world. It has a huge impact on a person’s life, self-esteem, and confidence and it can even have an impact on their employment prospects. As new studies come to light, updating your knowledge will allow you to better understand this condition as well as more successful ways of treating it.

The word atopic refers to someone with an allergic condition and dermatitis is associated with allergies. Topical steroids are prescribed and have been the mainstay of treatment for many years and still are. Phototherapy and systemic immune-suppressant drugs are used for the more severe cases.

Atopic dermatitis impacts 20% of infants and 3% of adults worldwide and is often associated with other diseases like allergic rhinitis and asthma. 

There has been a huge explosion of research related to atopic dermatitis, which has greatly changed the concept of the underlying pathogenesis of the disease. The research has also focused on gaining a better understanding of environmental issues that trigger the conditions, which are the external factors to the response component, which are internal factors.

Atopic dermatitis is prevalent in both males and females, although interestingly, studies show intrinsically that it exists more in females than males. Studies also confirm that if the condition develops in the early childhood years, there is a strong chance it will not continue through to adulthood and usually stops before puberty.  Though in severe cases the condition can be a lifelong disease.

Atopic dermatitis and epigenetics

When you research atopic dermatitis there are many studies that state that genetics play a very strong role in the pathogenesis of atopic dermatitis. In fact, it has been documented that 90% of the disease accounts for the early onset of atopic dermatitis.

It is important to note that there are three phases of atopic dermatitis: 

  1. the infantile stage
  2. the childhood phase, and
  3. the adult phase

all of which may have different severities.

Contributing Factors

For the skin to be intact we need to have a healthy barrier function. There needs to be structure in the epidermis and cell-to-cell adhesion proteins.  One of the main proteins is Filaggrin which is an intermediate filament-associated protein found in the stratum corneum.

If there is an absence of filaggrin, complications to the barrier function occur resulting in it becoming dry, and sore and can lead to infection.

Filaggrin gene mutations are often the strongest genetic risk of atopic dermatitis although, there are also studies suggesting that most patients with atopic dermatitis do not carry this mutation.

There are several genes that are involved in the development of atopic dermatitis, however, in very rare cases atopic dermatitis is caused by inherited mutations in a single gene.

The skin’s microbiome

Our skin is a large ecosystem of microorganisms that can influence the pathogenesis of inflammatory dermatosis or skin lesions. The Th17-immune response is a pro-inflammatory immune pathway associated with autoimmune diseases.

Th17 cells belong to the T-Lymphocyte group and are pro-inflammatory cells that secrete substantial amounts of interleukin 17A.

The skin microbiota promotes normal skin homeostasis through a Th17 cell immune response and secretion of antimicrobial peptides that nourish the commensal flora.

This all helps to prevent the growth of pathogenic species such as Staphylococcus aureus.

Another bacteria Staphylococcus epidermidis is a commensal bacterium that suppresses inflammation after skin injury and increases the innate immunity response. These bacteria also restrict the growth and reproduction of pathogenic gram-positive species through competition for resources and secretion of antimicrobial peptides. When the bacteria Staphylococcus aureus is able to colonize abnormally there is a breakdown in the skin and an increased risk of atopic dermatitis. 

Environmental allergens, such as house dust mites, fungi, pollen, and cats (especially) contain serine and cysteine proteases. These proteases are derived from Staphylococcus aureus and are capable of physically digesting the epithelial barrier, they then release enterotoxins, and induce pro-inflammatory cytokines.

There are studies showing that S. aureus is found on the skin of 90% of people with atopic dermatitis. This imbalance between commensal and pathogenic microbes is a hallmark of atopic dermatitis. During atopic dermatitis outbreaks, skin bacterial diversity is lowered with increased S. aureus and diminished S. epidermidis.

Read more in the latest edition of APJ journal