The hallmark symptoms of eczema, or atopic dermatitis, are dry, itchy skin and inflammation or rashes on various parts of the body, including the face, hands, feet, insides of the elbows, and behind the knees.
Numerous other diseases and conditions can also cause an itchy rash — from scabies to viral infections like chickenpox to bacterial infections like impetigo. But unlike these other examples, eczema is not caused by tiny mites or microbes that can be passed from person to person. "Atopic dermatitis, the most common type of eczema, is not contagious," explains Kanwaljit K. Brar, MD, a pediatric allergist and immunologist at NYU Langone in New York City.
Instead, atopic dermatitis is a chronic inflammatory skin condition, in which an immune system reaction causes symptoms to develop. The condition is associated with a wide range of potential risk factors, but its specific cause in any given person is unclear. (1)
Understanding the Causes and Symptoms of Eczema
The skin of people with eczema does not retain moisture well, causing it to become dry and lose its protective properties. When this occurs, various symptoms can develop:
- Patches of skin that are rough and leathery or scaly
- Swollen skin
- Skin color changes (1)
- Increased lines on the palms of the hands and feet
- Dry, pale patches on the face and upper arms
- Small bumps on the upper arms and thighs (2)
Rather than a single factor being behind the development of atopic dermatitis, research suggests that eczema is a complex condition involving genetics, skin barrier function, allergies, immune system dysfunction, and environmental factors. (3,4)
What's more, the symptoms of atopic dermatitis typically arise from specific and varied triggers, including dry skin (from weather changes, for example), a wide range of irritants like common cleaning products and fabrics, and stress. (5)
How Genetics Play a Role in Eczema and Atopic Dermatitis
The word "atopic" in atopic dermatitis indicates an association with allergies. Though the condition isn't always directly caused by an allergic reaction, it is commonly associated with other allergic conditions.
In fact, atopic dermatitis is often the start of the so-called "atopic march," in which a person then develops food allergies, hay fever, and asthma. It's estimated that up to 60 percent of people with atopic dermatitis develop asthma or hay fever and up to 30 percent have food allergies.
As with other allergic disorders, atopic dermatitis tends to run in families. Having a parent with atopic dermatitis, hay fever, or asthma increases a person's risk of getting the skin condition. (6) But, Dr. Brar notes, atopic dermatitis can also develop without a demonstrated family history for atopic conditions.
Research suggests that a number of genes are associated with the development of atopic dermatitis. One gene with the strongest association is FLG, which encodes a protein, called filaggrin, that is important for creating a strong skin barrier to keep water in and foreign substances out.
About 20 to 30 percent of people with atopic dermatitis have a mutated or altered FLG gene, compared with 8 to 10 percent of people without atopic dermatitis, according to the National Library of Medicine. Other skin-related genes, such as SPINK5/LEKT1, are also associated with atopic dermatitis.
In very rare cases, atopic dermatitis may arise from the mutation of a single gene: CARD11. A mutation in this gene can result in abnormalities in certain immune system cells. (4,6)
Common Risk Factors for Eczema and Atopic Dermatitis
Aside from genetics and family history, other risk factors for eczema may exist.
Some research suggests that boys are more likely than girls to develop atopic dermatitis during infancy, and this pattern switches in adolescence. (7) Other research suggests that the prevalence of atopic dermatitis is higher among people of African ancestry. (8)
Various other risk factors may also exist, though the data is still inconclusive. Specifically, these potential risk factors include:
- Living in a developed country, a city, or a cold climate
- Being born to a mother who is older (or later in her childbearing years)
- Being born into a higher social class or to parents with higher education
- Being born by Cesarean section
- Being exposed to secondhand smoke
- Being overweight
- Having a high birth weight
- Being treated with antibiotics in infancy
- Being exposed to hard water in infancy
On the opposite side of things, some factors may be protective against atopic dermatitis. "Early moisturizer use in infants may reduce a person’s risk of atopic dermatitis," Brar says. Others may include:
- Being breastfed within the first three months of life (delayed weaning may increase risk)
- Being exposed to a child day-care setting
- Drinking unpasteurized farm milk during the first two years of life
- Being exposed to farm animals (both during pregnancy and after birth)
- Having pets (specifically dogs) early in life (4,7,8,9)
Eczema in Children: A Connection to Food Allergies
Specific foods do not cause eczema. (9)
But food allergies go hand in hand with atopic dermatitis, thanks to the atopic march. About 50 to 70 percent of children with early onset atopic dermatitis have one or more allergies, mainly food allergies, the most common of which are cow's milk, hen's eggs, and peanuts. (4)
What's more, becoming sensitized to food earlier in life may result in more severe atopic dermatitis later in life. And food avoidance (in the absence of an existing food allergy) increases the likelihood of developing new food reactions in the future.
Food allergies can also make atopic dermatitis worse and can be triggers for symptom flares. That is, the skin lesions of atopic dermatitis are sometimes the result of an inflammatory response to the food allergens. (3,4,8)
But some research suggests that high consumption of fish during pregnancy decreases the risk of atopic dermatitis in children, as does consuming fish late in infancy. (4)
Can Diet Triggers Cause Eczema in Adults?
As with children, food does not cause eczema in adults, but food allergies can trigger eczema symptom flares.
Research shows that cutting out specific foods from a person's diet does not reduce atopic dermatitis symptoms unless that person has a known allergy to that food.
Common Eczema Triggers That Can Cause Flares
The symptoms associated with eczema are not present at all times. Rather, people with atopic dermatitis go through periods of flare-ups (increased symptoms) followed by remissions (no physical signs of the condition).
Eczema flares are caused by triggers. These eczema triggers may include a wide range of irritants, allergens, and other substances:
- Soaps, detergents, shampoos, and dishwashing liquids
- Bubble bath liquids
- Pet dander
- Dust mites
- A hot or dry climate
- High or low humidity
- Bacterial, viral, or fungal infections (5)
- Dust or sand
- Cigarette smoke
- Perfumes and cosmetics
- Wool or synthetic fabrics
- Chemicals and cleaning solutions (12)
- Allergenic foods, such as milk, eggs, peanuts, soy, wheat, and fish (13)
Editorial Sources and Fact-Checking
- What Is Eczema? National Eczema Association.
- Thomsen SR. Atopic Dermatitis: Natural History, Diagnosis, and Treatment. ISRN Allergy. April 2014.
- McPherson T. Current Understanding in Pathogenesis of Atopic Dermatitis. Indian Journal of Dermatology. November-December 2016.
- Nutten S. Atopic Dermatitis: Global Epidemiology and Risk Factors. Annals of Nutrition & Metabolism. April 2015.
- Eczema Causes and Triggers. National Eczema Association.
- Atopic Dermatitis. Genetics Home Reference. October 2017.
- Pyun BY. Natural History and Risk Factors of Atopic Dermatitis in Children. Allergy, Asthma & Immunology Research. March 2015.
- Fuxench ZCC. Atopic Dermatitis: Disease Background and Risk Factors. Advances in Experimental Medicine and Biology. October 2017.
- Atopic Dermatitis: Causes. American Academy of Dermatology.
- Bath-Hextall FJ, Delamere FM, Williams HC. Dietary Exclusions for Established Atopic Eczema. Cochrane Systematic Review. January 2008.
- Dhar S, Srinivas SM. Food Allergy in Atopic Dermatitis. Indian Journal of Dermatology. November-Dececember 2016.
- Patient Education: Eczema (Atopic Dermatitis) (Beyond the Basics). UpToDate. July 2021.
- Eczema: Triggers. National Jewish Health. February 2018.