What Causes Atopic Dermatitis?

There is no one single cause for atopic dermatitis (also called eczema). Instead, experts think many different factors occur at once and all play a role. Each person’s case is different. And in some cases, the underlying causes may not be as clear as for others.^1-3

Some causes, like allergens or irritants, can be avoided. Others, like genetics or immune system issues, cannot. Experts have identified a few potential causes of eczema. But research is currently underway to learn more about what might cause the condition and how.³

Issues with the skin barrier

The skin is your body’s first line of defense. It keeps out allergens and germs. It also helps maintain your water balance. A strong skin barrier can help hold in fluid and also allows you to sweat when needed.^1-4

The top layer of the skin is called the epidermis. When the epidermis is damaged or not as strong as it should be, skin dryness, infection, and inflammation can occur. These changes then lead to eczema symptoms.^1-4

There are several ways the skin barrier can be damaged. In some people, the filaggrin gene (FLG) is changed (mutated) so that it does not work normally. The protein made by the filaggrin gene normally helps maintain a strong top layer of skin. Changes to the gene may lead to a weak skin barrier. This type of gene mutation can run in families.^1-4

Also, proteins called enzymes can be out of balance in the skin. These proteins perform many important functions that keep the skin strong. Without these enzymes, the skin may become weaker and less able to regulate water.^1,4

There are also tiny protein channels in skin cells that allow water or other important nutrients to pass through while keeping germs out. These channels may not be working correctly. This can lead to skin breakdown and inflammation.^1,4

Immune system changes

There are many different parts of the immune system involved in eczema. Some experts think eczema is the result of the immune system being too aggressive. It may overreact to allergens or germs that get into the body through the weakened skin barrier. And an overactive immune system can further weaken the skin barrier.^1-4

Certain immune cells, proteins, and antibodies all play a role in creating inflammation. These may be in overdrive during eczema flares. Many of these cells and proteins also play a role in other atopic conditions that occur together, such as asthma and allergies.^1-4

The reason why the immune system may overreact in people with eczema is unknown. But it may be related to genetic or environmental factors.^1-4

Changes in skin bacteria

You typically have many different germs on your skin at all times. Many of these are not dangerous. Germs like bacteria that can cause infections are kept out by your skin.¹

However, in people with eczema, the types of germs on the skin can change. Instead of having many different types of germs, there is mainly 1 type. This germ (bacteria) is called Staphylococcus aureus (S. aureus or Staph aureus).¹

S. aureus can live on the skin without causing problems. But when too much of it is present, it can make proteins that damage the skin barrier or cause inflammation. S. aureus can also cause infection within areas of eczema where the skin is weaker or broken. Not much is known about why this change occurs, so researchers are actively studying it.¹

Overactive itch response

In order to perceive and scratch an itch, your body uses many different processes. Many of these are in the nervous system. Different chemicals and proteins help communicate to your brain that you are itchy. Then, your brain tells your motor system to scratch.¹

Some experts believe that the overactive immune system in people with eczema also causes an overactive drive to itch. The resulting scratching can lead to skin breakdown and worsening of eczema symptoms.¹

Environmental factors

There are also many factors in the environment that can increase your risk of developing eczema. These factors can also worsen your symptoms. They include:^1-5

• Being in a cold, dry environment that causes dry skin
• Living in an urban (city) area and being exposed to air pollution
• Using soaps or detergents with scented chemicals
• Wearing clothing made of irritating fabric (like wool)
• Being exposed to hard water (water with high levels of calcium in it)
• Being exposed to common food allergens or environmental allergens like dust mites
• Having high levels of emotional distress
• Swimming or taking baths and showers too often
• Environmental allergens like dust or pollen

One theory that not all experts support is called the “hygiene hypothesis." This proposes that a lack of exposure to germs, other kids, or pets early in childhood leads to a weak immune system.¹

The research about what causes eczema has had mixed results. It is not clear what exposures definitely lead to the development or worsening of eczema. It is also possible for a person to be exposed to many of these factors and not have any response. More research is needed to understand how the environment plays a role in eczema symptoms.