September 25, 2026 ยท Updated September 25, 2026
What causes eczema? Genes, skin and immune system
Nobody knows one exact cause of eczema. Genes, a weak outer skin layer, an overactive immune system and your surroundings all play a part.
By Nick, Founder of Skinli. Not a doctor. General education only.
Part of the Eczema, which puts every step in order.
Eczema is a group of skin conditions that make skin dry, itchy and inflamed, and only a doctor can confirm that a rash is eczema. This guide covers atopic eczema (also called atopic dermatitis), the most common type. The complete guide to eczema explains the condition as a whole. This page answers a narrower question: why does eczema start in the first place?
The short answer from the US National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) is that researchers do not know the exact cause. They do know that three things play a part: the genes you inherit, your immune system, and things in the world around you. Each of the three affects the outer layer of the skin, and that layer is where the problem shows.
The outer layer of skin lets water out
The outermost layer of your skin has two jobs. It holds water in, and it keeps everyday things out, such as dust, soap, pollen and germs. Doctors call this layer the skin barrier.
The American Academy of Dermatology (AAD) says that in people with atopic eczema, this layer has gaps. The gaps let too much water escape, which dries the skin. They also let irritants and germs get inside, which leads to redness, swelling and, at times, infection. The AAD adds that researchers have seen this happen and are still studying why it happens.
NIAMS describes the same chain of events. Changes in the protective layer cause the skin to lose moisture. The dry skin becomes damaged and inflamed. Newer research suggests the inflammation itself creates the feeling of itch. Scratching then damages the skin further and raises the chance of a bacterial infection. So itching leads to scratching, and scratching leads to more itching and more damage.
MedlinePlus, the health site of the US National Library of Medicine, says the same thing in one line: people with atopic dermatitis may be more sensitive because their skin lacks specific proteins that keep water in.
Genes: eczema often runs in families
Family history is the clearest risk factor. The NHS says you are more likely to have atopic eczema if one or both of your parents have it, or if you or a close family member has asthma or hay fever. The AAD says studies found this family link in 70 percent of people with atopic dermatitis. They had one or more blood relatives with atopic dermatitis or with an allergic disease such as asthma or hay fever.
One gene stands out. MedlinePlus Genetics names the FLG gene, which gives the body instructions for a protein the outer skin layer needs to stay strong and keep water in. Changes in FLG are found in 20 to 30 percent of people with atopic dermatitis, compared with 8 to 10 percent of the general population without it. When the protein is short, the outer layer of skin works less well and water escapes, which leads to dry skin.
A gene change raises the risk, and other factors decide whether eczema appears. MedlinePlus Genetics says that some people with a change in FLG, or in another gene linked to eczema, never develop the condition, and that things in the environment also play a part. It also says that some people with atopic dermatitis carry no known risk gene at all.
The immune system overreacts
The immune system normally fights germs such as bacteria and viruses. NIAMS explains that in atopic dermatitis, the immune system sometimes becomes confused and overactive, and that this creates inflammation in the skin. Inflammation is the redness, swelling, heat and itch that you see and feel.
This is also why many eczema medicines act on the immune system. NIAMS says steroid creams and ointments help to decrease inflammation. The AAD describes biologic medicines, which are given as injections, as drugs that target or quiet the part of the immune system that is overactive. A doctor decides whether any of these fit a person's eczema. The guide on how eczema is treated describes what a doctor may offer.
An autoimmune disease is one in which the immune system attacks the body's own tissue. Whether eczema fits that description is a common question, and it has its own guide: is eczema an autoimmune disease?
Things around you
NIAMS lists things in the environment that may push the immune system to weaken the skin barrier and let more moisture escape:
- tobacco smoke
- some types of air pollution
- fragrances and other ingredients in skin products and soaps
- skin that is too dry
Where you live seems to matter as well. The AAD says that around the world, people who live in cities are more likely to develop atopic dermatitis than people who live in rural areas. Several studies found this, and air pollution may be the reason. The AAD adds that living in a dry climate, or far from the equator where it is cooler, may also raise the risk.
The AAD also reports that in the United States, Black children are twice as likely as white children to develop atopic dermatitis, according to several studies. The same page says the condition develops in people of all ages and races.
How allergies fit in
Allergies and atopic eczema often appear in the same person, which is why many people believe one causes the other. MedlinePlus states that people with atopic dermatitis often test positive on allergy skin tests, and it also states that allergies do not cause atopic dermatitis. The AAD says that in most cases, atopic dermatitis is not caused or triggered by a specific allergy.
The link often runs in the opposite direction. The AAD estimates that one third of children with atopic dermatitis later develop asthma, and two thirds get hay fever. When these allergic conditions develop one after another, doctors call it the atopic march. The word "atopic" itself means linked to allergies, according to MedlinePlus Genetics.
Food needs its own mention. NICE, the UK body that writes guidance for doctors, says food allergy is sometimes linked to atopic eczema, especially in the youngest children. The NHS says not to change your diet unless a doctor tells you to, and it says this includes a mother who is breastfeeding a baby with eczema. If you think a food makes your skin or your child's skin worse, a doctor can arrange the right tests.
Can eczema be caught or prevented?
Eczema cannot be caught from another person. The NHS says atopic eczema is not contagious, so you cannot catch it or spread it. The guide is eczema contagious? explains which skin infections on top of eczema can spread.
Prevention is harder. In April 2026 the AAD published its first guidelines for children with atopic dermatitis. The guidelines found insufficient evidence or no benefit for early food introduction, breast milk, probiotic or vitamin D supplements, water softening and dust mite avoidance as ways to prevent eczema. Moisturizer was the only measure to receive a conditional recommendation for reducing eczema in children aged 6 months to 3 years. Parents who want to know whether this applies to their child should ask the child's doctor.
Why eczema can start in adulthood
Most atopic eczema starts in childhood. The AAD says most people who develop it do so by 5 years of age, but it can also begin at puberty or later. When it starts after a person's 18th birthday, dermatologists call it adult-onset atopic dermatitis, and a peak time for it is in a person's 50s.
Eczema that went away in childhood can also return. The AAD says it is possible for atopic dermatitis to go away in childhood and return years later, and that when it returns it is often milder.
Other types of eczema cause itchy patches in adults as well. The AAD names nummular eczema, contact dermatitis and neurodermatitis, and says each needs different treatment, so it is important to know which one you have. Contact dermatitis comes from something that touches the skin, such as a soap, a metal or a cosmetic. The guide to types of eczema covers each one.
A cause and a trigger are two different things
A cause explains why a person has eczema at all. A trigger is something that makes eczema that is already there flare up, which means the symptoms get worse for a time. Many people mix the two up, so it helps to keep them apart.
The NHS lists things that can make atopic eczema worse:
- contact with an allergen or irritant, such as soap, washing detergent, pets, some fabrics, pollen, house dust mites or certain foods
- heat or changes in temperature
- skin infections, such as a staph infection
- stress
- hormonal changes, such as during pregnancy
Avoiding a trigger can mean fewer flare-ups. The underlying tendency, which comes from genes, the immune system and the skin barrier together, stays in place. The guide to eczema flare-up triggers goes through each trigger and what the sources say about it.
What to do with this information
Knowing the causes helps in two practical ways. It explains why moisturizing matters so much, because moisturizer supports the outer layer of skin that lets water out. It also explains why a doctor asks about your family: eczema, asthma and hay fever in relatives make atopic eczema more likely.
If you have a new itchy rash, see a doctor. A doctor can confirm whether it is eczema, tell which type it is, and rule out other conditions that look similar. The NHS says to ask for an urgent appointment if eczema is blistered, crusty, leaking fluid, painful, swollen, warm, or getting worse fast, or if you have a high temperature, because these can be signs of infection.
Frequently asked questions
What causes eczema?
Eczema has no single known cause. The US National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) says researchers know that genes, the immune system and the environment all play a part in atopic dermatitis, the most common type. Together they change the outer layer of the skin so it loses water and lets irritants in, which leads to dry, inflamed, itchy skin. A doctor confirms whether a rash is eczema.
What causes eczema in adults?
Eczema in adults has the same main causes as in children: genes, an overactive immune system and things in the environment, according to NIAMS. The American Academy of Dermatology says atopic dermatitis can start after age 18, with a peak time in a person's 50s, and it can return in adults who had it as children. Adults also get other types, such as contact dermatitis, so a doctor should confirm which type it is.
Is eczema genetic?
Eczema is partly genetic. The NHS says you are more likely to have atopic eczema if one or both parents have it, or if a close relative has asthma or hay fever. MedlinePlus Genetics names the FLG gene as the strongest known link: it is changed in 20 to 30 percent of people with atopic dermatitis and in 8 to 10 percent of people without it. The environment also plays a part.
Why am I prone to eczema?
A person is prone to eczema when the outer layer of their skin holds water poorly and their immune system overreacts, says NIAMS. The American Academy of Dermatology links higher risk to family history, city living, a dry or cool climate, and, in the United States, being a Black child. The AAD says studies found a blood relative with eczema, asthma or hay fever in 70 percent of people with atopic dermatitis.
Is eczema caused by allergies?
Allergies are not the cause of most atopic eczema. MedlinePlus says people with atopic dermatitis often test positive on allergy skin tests, yet states that atopic dermatitis is not caused by allergies. The American Academy of Dermatology says that in most cases it is not caused or triggered by a specific allergy. Allergies often develop alongside it: the AAD estimates one third of children with atopic dermatitis later get asthma.
Is eczema caused by food allergies?
Food allergy is linked to eczema in some people. NICE, the UK body that writes guidance for doctors, says food allergy is sometimes associated with atopic eczema, particularly in the youngest children. The NHS says not to change your diet unless a doctor tells you to, and this includes mothers who breastfeed a baby with eczema. A doctor can arrange allergy tests when a food seems to cause reactions.
Is eczema caused by bacteria?
Bacteria are missing from the list of causes that NIAMS gives for atopic dermatitis, which names genes, the immune system and the environment. Bacteria can make eczema worse. The NHS lists skin infections, such as a staph infection, among things that worsen atopic eczema. The American Academy of Dermatology says yellow or golden crusts on eczema often mean a staph infection, and a doctor should check them.
Is eczema caused by dry skin?
Dry skin is part of how eczema develops, and it also makes eczema worse. NIAMS explains that changes in the skin's protective layer make it lose moisture, and the dry skin then becomes damaged and inflamed. NIAMS also lists skin that is too dry among the environmental factors linked to atopic dermatitis. Ordinary dry skin and eczema look alike at times, so a doctor tells them apart.
Which vitamin deficiency causes eczema?
NIAMS, the NHS and the American Academy of Dermatology name no vitamin deficiency as a cause of eczema. Their pages point to genes, the immune system and the environment. The AAD's 2026 guideline for children found insufficient evidence or no benefit for vitamin D supplements to prevent eczema. NICE guidance for children says food supplements have not yet been properly tested for eczema in clinical trials.
Why have I started getting eczema?
New eczema in an adult can be atopic dermatitis starting late, childhood eczema coming back, or a different type. The American Academy of Dermatology says adult-onset atopic dermatitis peaks in a person's 50s, and eczema that went away in childhood can return years later. Contact dermatitis, caused by something that touches the skin, is another common cause of a new rash. A doctor can tell which type it is.
What causes eczema in babies?
Eczema in babies has the same broad causes as in older people: genes, the immune system and the environment, according to NIAMS. The American Academy of Dermatology says atopic dermatitis often appears between 2 months and 5 years of age, and a baby has a higher risk when one or both parents have eczema, asthma or hay fever. A doctor should check any rash on a baby and advise on care.
Who is most likely to get eczema?
People with a family history of eczema, asthma or hay fever are the most likely to get atopic eczema, say NIAMS and the NHS. The American Academy of Dermatology adds that in the United States, Black children are twice as likely as white children to develop it, and that people who live in cities get it more often than people in rural areas. It usually starts before age 5.
Sources
- Atopic Dermatitis: Overview, Symptoms, and Causes (National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIH))
- Eczema types: Atopic dermatitis causes (American Academy of Dermatology)
- Atopic dermatitis (MedlinePlus Genetics, U.S. National Library of Medicine)
- Atopic dermatitis (MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine)
- Atopic eczema (NHS)
- Can you get eczema as an adult? (American Academy of Dermatology)
- Atopic eczema in under 12s: diagnosis and management (CG57) (National Institute for Health and Care Excellence)
- American Academy of Dermatology issues first-ever pediatric atopic dermatitis guidelines (American Academy of Dermatology)
- Eczema types: Atopic dermatitis symptoms (American Academy of Dermatology)
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A doctor can tell you what this is.
Skin that hurts, spreads, bleeds, weeps or does not get better needs a doctor or a dermatologist. They can confirm what it is and offer treatment that needs a prescription.
Skinli gives general education about eczema and cannot diagnose eczema or any other rash. See a doctor for any rash on a baby, and get urgent care for a rash that spreads fast, blisters, weeps, crusts, feels hot or painful, or comes with a fever.