What Is the Atopic March?

What Is the Atopic March?

The atopic march, or allergic march, refers to the progression and accumulation of atopic conditions as an individual (usually a child) gets older. Much more research needs to be done to understand the true complexity of the atopic march, however, many experts have been theorizing on what it is and why it happens since the 1920’s, when it was first proposed by allergists A.F. Coca and R.A. Cooke.1 Since then, the atopic march has continued to be studied and potential prevention tactics have been suggested.

What is the atopic march?

The atopic march occurs when an individual develops multiple atopic (allergic) conditions as they age. These atopic conditions include atopic dermatitis, food allergies (such as allergies to milk, soy, eggs, and peanuts), allergic rhinitis, and asthma. The order of the march is not concrete, however, the first stop in the path is generally atopic dermatitis, followed by food allergies, and finally ending in asthma and/or allergic rhinitis (hay fever).1 A growing body of evidence points toward a relationship between the severity as well as the age of onset of atopic dermatitis (the first stop) and the risk of developing the remaining atopic conditions along the march. Essentially, the common trend demonstrated is that the younger an individual is when they are diagnosed with atopic dermatitis, and/or the more severe or persistent their atopic dermatitis is, the greater the chance they will continue down the atopic march to eventually develop asthma and/or rhinitis.2

It is important to note, however, that not everyone with atopic dermatitis will progress through the atopic march. Some individuals will only have atopic dermatitis, or atopic dermatitis with just one of the other atopic conditions in the march. Additionally, it’s not uncommon for individuals to have conditions that normally present near the end of the march, like asthma or allergic rhinitis, without one or more of the earlier conditions.

When does the atopic march occur?

The march can occur at any time; however, it occurs most frequently in early childhood, with atopic dermatitis being diagnosed as early as six months old or younger. Although the march could happen at any point throughout an individual’s life, most experts consider it to be exclusive to childhood. Peak diagnostic times for each of the atopic conditions have been estimated to be less than a year of age for atopic dermatitis, right around a year for food allergies, between a year and 18 months for asthma, and two years for allergic rhinitis. These numbers alone can provide a picture of a potential march timeline for an infant.1

The chance of being diagnosed with one or more of these atopic conditions decreases greatly with age, with the minority of cases being diagnosed in adulthood. This also paves the way for the march to take place primarily in children and young adults. Further, and for reasons not well understood, the atopic conditions within the march can also decrease in severity or completely go away as an individual gets older. Essentially, some people will “outgrow” the march. However, more research is needed to determine why this can sometimes occur.1,2

What causes the atopic march?

As mentioned, the cause of the atopic march is not completely understood. The atopic march is thought to have several potential genetic and environmental factors that could potentially lead to its development and progression. One common theory amongst experts suggests that a defective skin barrier may provide the pathway for allergens (including those related to food) and other pathogens to invade the body.1,2 For example, an infant with severe atopic dermatitis and a broken skin barrier may take in foreign particles easier, and trigger an immune response that will eventually lead to a food allergy the next time they come in contact with that kind of particle. This may be the reason why some babies are allergic to cow’s milk and show signs of an allergic reaction when trying cow’s milk for the first time or one of the first times. If they have atopic dermatitis and a broken skin barrier, they may have already been exposed to the potential allergen or one of its components through their skin and their body mounted an immune response to prepare for the next time they encountered it. This same idea can also be expanded to other allergens, such as dust.

Additionally, the broken skin barrier can help pave the way for colonization of the skin by pathogens like staphylococcus aureus (S. aureus) which not only contributes to the itching and inflammation of the skin, but can also induce an immune-system response with widespread inflammation that can eventually affect the airways. Further, certain mutations in the skin barrier have been identified as potentially contributing to the atopic march, as well as the inappropriate responses of several immune system-related processes in the body. Aside from genetics, there have also been theories surrounding environmental triggers leading to the development of the atopic march. Ultimately, much more investigation is needed to understand this complex process.2

What can be done about the atopic march?

Similar to our understanding of the causes of atopic march, ways of preventing it or stopping it once it begins are also inconclusive. Finding a way to repair the skin barrier or protect the skin from invaders has been a common suggestion in recent years.1,2 Some suggest that there is a critical window of time during infancy that this needs to occur for the atopic march to be prevented, while others suggest that controlled exposure, including oral exposure, to potential allergens at key times may decrease an individual’s risk of being hypersensitive to them later on.1

Additionally, it has been suggested that administering medications like antihistamines or immunotherapy to children in early stages of the atopic march (or who have a high risk of starting the atopic march) may help reduce the chances of progression. An allergist or other healthcare professional may be able to assess the potential genetic and environmental risk factors an individual might have that could lead to progression of the atopic march. Identifying these risk factors may lead to more individualized treatment or prevention options.

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