What Causes Eczema (Dermatitis)?

Medically reviewed by William Truswell, MD

Eczema (also known as dermatitis) is a group of skin conditions with no single known cause. Generally, it's influenced by your genes, environment (such as where you live), and your immune system. Your immune system plays a part by reacting strongly to perceived threats (which is known as an overactive immune response), triggering the irritating skin symptoms that characterize each type of eczema.

Things like harsh soaps and allergens like pollen can trigger worsening symptoms. Other triggers include temperature changes, stress, and skin infections. While there's no cure, you can manage eczema by avoiding triggers, using moisturizers, and sometimes taking medicines.

While there isn't a singular cause of eczema, researchers have identified risk factors and triggers can can contribute to each type of eczema. Below, we'll briefly describe each type of eczema and what is known about their respective causes.

Atopic Dermatitis

Atopic dermatitis (also called atopic eczema) is the most common type of eczema and usually starts in childhood. With atopic dermatitis (also called atopic eczema), your immune system is overactive and highly sensitive to potential allergens. It is likely due to a combination of different factors, such as environmental variables or gene mutations that affect your skin or immune cells.

One common mutation can cause a specific skin protein called filaggrin to not work properly. This leads to a dysfunctional skin barrier that’s more prone to moisture loss (and dryness), making it easier for microorganisms and harmful substances to pass through the skin. Not everyone with atopic eczema has this filaggrin mutation, as there are various subtypes of the condition, each with different underlying causes.

In general, if you have atopic eczema, you may be more prone to skin infections from bacteria, fungi, or viruses.

Common allergens that can trigger atopic eczema are nickel, fragrances, mites, and certain foods like peanuts and milk. Stress, air pollution, and sweating may also lead to symptoms. Some people with atopic dermatitis can also have other allergic conditions, such as asthma or hay fever (allergic rhinitis).

Contact Dermatitis

There are two main types of contact dermatitis: allergic and irritant. Both types produce similar eczema symptoms, but they have different causes.

With the allergic type, your skin is sensitive to an allergen (a usually harmless substance), and your immune system attacks the allergen—mistaking it for a toxic invader—and your skin develops a rash.

In the United States, the most common type of allergic contact eczema is poison ivy. Other common contact allergens include nickel, metal alloys, fragrances, lanolin (wool grease), essential oils, and ingredients in skin and hair products, such as parabens (a preservative) and benzophenones (which is commonly found in chemical sunscreens).

For irritant contact eczema, an irritant—often a chemical substance—damages the outer layer of your skin and your immune system tries to repair it. Whether your symptoms are mild to severe depends on how long your skin is in contact with the substance, as well as how potent and concentrated the irritant is.

Related: Editors' Pick: Top Mineral Sunscreens for Sensitive Skin

Seborrheic Dermatitis

Seborrheic dermatitis is a type of eczema that affects the scalp and is often referred to as dandruff. People with seborrheic eczema tend to have a higher amount of Malassezia, a type of yeast that naturally lives on healthy skin (even without eczema). The yeast survives off the fats in your skin’s sebum—the oily substance produced in your skin's sebaceous glands to help keep your skin hydrated.

More research is needed to determine what causes seborrheic dermatitis. However, researchers have identified factors that may raise your risk of developing it. This includes a genetic predisposition, immunosuppression (such as with HIV/AIDs or other health conditions), a dysfunctional skin barrier, and certain medications. Stress and cold, dry weather can also lead to a flare-up (worsening of symptoms).

Dyshidrotic Dermatitis

Dyshidrotic eczema (also called dyshidrosis) causes small blisters on the palms of hands, fingers, feet, and toes.

You can be predisposed to developing dyshidrotic dermatitis, especially if you already have atopic eczema, allergic contact dermatitis, fungal infections, or hyperhidrosis (a condition characterized by excessive sweating). Some factors that could trigger worsening dyshidrotic eczema are cold, dry weather, and skin contact with nickel alloys (in dental braces and some jewelry).

Nummular Dermatitis

Nummular dermatitis—also called discoid eczema or nummular eczema—presents as many small, circular rashes or sores.

Nummular dermatitis is especially common in areas that have been recently injured. It has also been linked to several factors, such as having sensitivity to allergens, skin dryness, or breast implants, along with being in dry environments and taking certain medications, including certain antivirals and acne medication. Your symptoms can get worse when your skin’s natural moisture is off balance, such as from prolonged hot showers.

Stasis Dermatitis

Statis dermatitis is inflammation in areas of fluid buildup—usually the legs. High blood pressure in the veins (venous hypertension) and resulting poor blood flow can cause stasis dermatitis. You can have venous hypertension when your veins have difficulty pumping blood back to your heart. Excess pressure in the lower legs can lead to skin changes and more white blood cell activity.

Having poor blood flow in the veins (chronic venous insufficiency) and enlarged veins (varicose veins) can raise your risk of stasis dermatitis. Other risk factors for these leg conditions include having obesity, a family history of these conditions, and prior vein clots deep in the leg (deep vein thrombosis).

Asteatotic Dermatitis

Asteatotic dermatitis—also known as eczema craquelé or xerosis—is a type of eczema that causes itchy, dry, scaly skin. It is caused by water loss through your skin barrier. This condition is most common in older adults with dry skin, as an aging skin barrier loses moisture more easily and produces less sebum and sweat. Symptoms can also worsen in cold, dry environments and with frequent exposure to detergents, which can strip your skin of natural oils.

Neurodermatitis

True to its name, neurodermatitis may have an underlying psychological cause. You may find that emotional stress can lead to that urge to scratch or rub the itchy patches, resulting in more itchiness and subsequent scratching.

People with chronic itch conditions can feel relieved when scratching even when the skin isn’t itchy, according to a 2015 brain imaging study. However, more research is needed to further understand what causes the itch-and-scratch cycle of neurodermatitis.

Some people who have dysfunctional skin barriers or other skin conditions—like atopic dermatitis, contact eczema, or psoriasis—can develop neurodermatitis. Mental disorders like anxiety, depression, and obsessive-compulsive disorder (OCD) can also lead to symptoms of neurodermatitis.

A Quick Review

Eczema—a skin condition that generally causes skin inflammation, dryness, and itching—doesn't have one clear cause. Not only are there various factors that can contribute to the development of eczema, but the causes can also vary depending on the type of eczema you have.

Overall, eczema is likely caused by a mix of your genetics, your environment, and how your immune system works, but more research is needed.

If you think you have eczema, it's worth talking to a dermatologist (a doctor who specializes in the hair, skin, and nails) to ensure you're being properly diagnosed and can get on the right treatment path.

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