The Differences Between Eczema and Psoriasis

Both eczema and psoriasis are chronic skin diseases that cause red, dry, scaly skin rashes. Although they share similar signs and symptoms, their underlying causes are different. As a result, the ways in which the diseases are treated can also differ– sometimes significantly.

Given this, it is important that you get a formal diagnosis if you suspect eczema or psoriasis. Fortunately, there are ways your doctor can differentiate the two diseases so that they can be treated appropriately and effectively.

Symptoms

Eczema and psoriasis are both characterized by the appearance of patches of inflamed, dry skin, often in recurrent episodes known as flares. These similarities can make differentiating the disease difficult, especially in children.

In fact, according to a 2015 review of studies in the Journal of Clinical Medicine, eczema was the condition most commonly misdiagnosed as psoriasis in infants and adolescents (and vice versa).

That said, to the trained eye, the differences in symptoms can be striking. There are several tell-tale signs a dermatologist will look for.

Location

Eczema, also known as atopic dermatitis, tends to be constrained to the crook of the elbows and the backs the knees, both of which are considered flexural surfaces. Psoriasis tends to affect the extensor surfaces, like the outside the forearms and elbows or the fronts of the knees and shins.

Psoriasis can also affect the scalp, face, ears, neck, navel, arm, legs, feet, hands, ankles, and lower back. Eczema can do the same, but perhaps not as aggressively.

The one area where the two diseases differ significantly is the nails. While both diseases can cause ridges, discoloration, and thickening, the pitting of the nail plate is characteristic of psoriasis, but not eczema.

Appearance

Both eczema and psoriasis can manifest with dry, red patches of thickened skin. With eczema, there may be rash, swelling, bumps, and generalized areas of darkened, leathery skin. Severe eczema might even ooze and crust over.

In contrast, psoriasis manifests with well-defined patches of reddened skin covered with fine, silvery-white scales (referred to as plaques). The plaques can bleed easily when scratched, leaving behind a pinpoint pattern of blood spots known as the Auspitz sign.

Scaling can occur with eczema, but doesn't always. With psoriasis, the scaling is characteristic and distinctive.

Itching

Pruritus (itching) can occur with psoriasis, but is more pervasive and generally more severe with eczema.

With psoriasis, the itching is believed to be caused by the inflammatory stimulation of nerve receptors in the skin called nociceptors. The same occurs with eczema but is further aggravated by the presence of immunoglobulin E (IgE), an antibody linked to allergy. Unlike eczema, IgE is not associated with psoriatic diseases.

Causes

Both eczema and psoriasis are inflammatory skin issues, meaning that inflammation is the primary cause of the dermatological symptoms. However, the mechanisms that cause the inflammation in each condition are extremely different.

Eczema Mechanisms

Eczema is believed to be the result of an overactive immune system. For reasons not entirely understood, the immune system suddenly malfunctions and stimulates the excessive production of white blood cells known as T-cells. T-cells are responsible for instigating the inflammatory response used to defend the body against infection.

With eczema, the excessive inflammation causes cells in the lymph nodes to release IgE into the bloodstream. The IgE response, in turn, causes epidermal cells to swell abnormally, leading to the formation of papules (bumps), vesicles (fluid-filled pockets), and lichenification (thickening of tissues).

Psoriasis Mechanisms

By contrast, psoriasis is an autoimmune disease in which the inflammation is targeted and specific. With psoriasis, the immune system suddenly regards skin cells as harmful and launches a defensive T-cell response.

The targets of the assault are immature skin cells, known as keratinocytes. The ensuing inflammation causes the cells to divide at an accelerated rate, turning over every three to five days rather than the usual 28 to 30 days.

Because the cells are being produced faster than they can be shed, they begin to push to the surface and form the characteristic psoriasis lesions.

Environmental Triggers

Both eczema and psoriasis are believed to be caused by a combination of genetics and environmental triggers. While scientists have started to identify specific mutations linked to certain diseases, there remains a considerable gap in understanding of the underlying genetics.

Far more is known about the environmental triggers that incite eczema and psoriasis symptoms. The list of triggers, while expansive, is also distinctive.

With eczema, a condition influenced by IgE, common allergens can trigger episodic flares. These include:

• Dust mites
• Pet dander
• Pollen
• Mold
• Dairy products
• Eggs
• Nuts and seeds
• Soy products
• Wheat 

Stress is also known to influence eczema.

With psoriasis, the triggers are less specifics but are known to incite flares in other autoimmune diseases. These include:

• Stress
• Infections
• Alcohol
• Smoking
• Skin trauma (referred to as the Koebner response)
• Certain medications, including beta-blockers, lithium, and antimalarials

A common trigger for both eczema and psoriasis is extremely cold/dry or extremely hot/humid weather.

Diagnosis

There are neither blood tests nor imaging studies that can definitively diagnose eczema or psoriasis. The diagnoses are primarily based on a physical examination and a review of your medical history.

If a diagnosis cannot be reached, a dermatologist may obtain a skin sample via biopsy to help differentiate the diseases. Under the microscope, the differences will be distinct:

• With eczema, the inflammation causes spongiosis (the swelling of the epidermis). Under the microscope, there will be large spaces between the skin cells along with visible papules and vesicles.
• With psoriasis, the inflammation causes the hyperproduction of keratinocytes. Under the microscope, the skin cells will appear acanthotic (compressed and thickened).

Treatment

Many of the same treatments are used for eczema and psoriasis. While the aims of treatment are similar—to reduce inflammation and relieve dermatological symptoms—the indications and response rates can vary enormously.

Common approaches include emollient-rich moisturizers, topical corticosteroids, oral antihistamines (to reduce itching), and the avoidance of known triggers.

Treatments are known to diverge in the following specific areas:

• Immunosuppressant drugs: Methotrexate and cyclosporine, used to suppress the immune system as a whole, are indicated for treating severe eczema only. The drugs can be used to treat moderate to severe cases of psoriasis.
• Phototherapy: Ultraviolet (UV) light therapy, also known as phototherapy, is considered an integral tool for treating moderate to severe psoriasis. There is only tentative support for the use of phototherapy in treating eczema.
• Topical calcineurin inhibitors: Protopic (tacrolimus) and Elidel (pimecrolimus) are calcineurin inhibitors that block the activation of T-cells. The drugs are approved by the U.S. Food and Drug Administration (FDA) for the treatment of eczema. They can also be used for psoriasis, but only off-label (without official FDA approval).
• TNF inhibitors: Tumor necrosis factor (TNF) inhibitors like Humira (adalimumab) and Enbrel (etanercept) block a key inflammatory compound associated with psoriasis. The inflammatory compounds primarily associated with eczema are interleukins. Not only are TNF inhibitors not approved for the treatment of eczema, but they can make the symptoms worse.

For these and other reasons, it is never a good idea to self-diagnose and self-treat a skin condition. Not only might you treat it inappropriately, but you could also miss a potentially more serious disease like lupus or skin cancer.