Atopic and contact dermatitis: how they differ

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Atopic dermatitis and contact dermatitis are very common types of eczema, a skin condition that can cause an itchy, scaly, inflammatory rash.

Although their symptoms are similar, they have very different causes. Atopic dermatitis is a chronic skin disorder characterized by inflammation of the skin (dermatitis). Most cases of atopic dermatitis are believed to arise from a combination of genetic and environmental factors. Contact dermatitis develops when the skin comes into contact with something that triggers a reaction. Correctly identifying the type of eczema is the key to proper treatment.

In some cases, the difference between the two is obvious; otherwise it is not. Some patients may even have atopic and contact dermatitis at the same time, making evaluation of the condition difficult.

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Symptoms

Both atopic and contact dermatitis can go through three different stages of eczema.

During the acute phase , the first of the three, both types of dermatitis cause an itchy red rash that may ooze or discharge a clear fluid. Contact dermatitis can develop small fluid-filled blisters (called vesicles), while oozing plaques (raised, wide areas of skin) are more common with atopic dermatitis. Although both conditions cause severe itching during this phase, contact dermatitis is more likely to cause pain and burning as well. If there is any difference in the case, it usually happens at this stage.

It is during the next phase, the subacute phase , that it is especially difficult to distinguish atopic dermatitis from contact dermatitis. In both cases, the rash is rough, dry, and scaly, often with superficial papules (small red bumps).

In both cases, the chronic stage is characterized by lichenification, a scaly, leathery thickening of the skin resulting from chronic scratching.

Since these phases are not specific and the contrasts may or may not be pronounced, it can be difficult to distinguish contact dermatitis from atopic dermatitis by the appearance of the rash alone. Some additional considerations come into play here.

Location

The location of the eczema rash is an extremely important clue in differentiating between atopic and contact dermatitis.

Atopic dermatitis most commonly affects flexed areas of the skin, such as the ulnar folds (antecubital fossa), behind the knees (popliteal fossa), the front of the neck, the folds of the wrists, ankles, and behind the ears.

Since atopic dermatitis begins with itching, which causes a rash when scratched, it is logical to assume that the affected area is the easiest to scratch. The areas of curvature are affected more often in older children and adults, but less often in infants, simply because it is difficult for them to scratch those specific areas. In contrast, very young children tend to develop atopic dermatitis of the face, elbows, and feet.

On the other hand, contact dermatitis occurs at the site of allergen exposure and therefore can occur practically anywhere on the body. These are often areas that are not usually affected by atopic dermatitis; for example, on the stomach (from nickel snaps on pants), under the armpits (from antiperspirants), and on the arms (from wearing latex gloves).

Age

The age of a person with an eczematous rash can also be a major difference between the two conditions. Most people who develop atopic dermatitis are 5 years old or younger, while contact dermatitis is less common in young children .

Although atopic dermatitis may appear for the first time in adulthood, contact dermatitis is much more common in adults .

While not a symptom in and of itself, age can help put symptoms in context.

Symptoms of Atopic Dermatitis.
Symptoms of contact dermatitis

Causes

Perhaps the most significant difference between atopic and contact dermatitis is human susceptibility.

Mechanism of atopic dermatitis

A person with atopic dermatitis often has a genetic mutation in a skin protein called filaggrin. The filaggrin mutation leads to the destruction of the barriers between the epidermal cells of the skin.

This leads to dehydration of the skin, as well as the ability of airborne allergens, such as pet dander and dust mites, to penetrate the skin. These aeroallergens cause allergic inflammation and intense itching. Scratching further erodes the skin and increases inflammation and itchiness.

An underlying tendency to allergies can also cause eczema to develop as a result of eating foods a person is allergic to, causing T-lymphocytes (a type of white blood cell) to migrate to the skin and cause allergic inflammation. . Without these basic predispositions, a person is unlikely to develop atopic dermatitis .

Mechanism of contact dermatitis

On the other hand, contact dermatitis is the result of a reaction to a chemical attack directly on the skin. This occurs among the majority of the population as a result of interaction with poison oak , poison ivy, or poison sumac (approximately 80% to 90% of people react to contact with these plants). Contact dermatitis is also common with exposure to nickel, cosmetics, and hair dyes.

Contact dermatitis is not caused by an allergic process, but the result of a delayed-type hypersensitivity mediated by T lymphocytes.

Causes of atopic dermatitis.

  • Genetic predisposition

  • Common in people with allergies and asthma.

  • Triggers include stress, skin irritation, and dry skin.

Causes of contact dermatitis

  • Local exposure to a hazardous substance

  • Delayed-type hypersensitivity reaction

  • Triggers include nickel, poison ivy / poison oak, and latex.

Diagnostics

Despite the similarities between the rashes, both atopic dermatitis and contact dermatitis are primarily diagnosed by visual examination and a detailed medical history. The age of the victim and the location of the rash, as well as the focused eye of your healthcare provider, are used to help distinguish between the two conditions.

In some cases, testing may be required.

A diagnosis of atopic dermatitis involves eczema, itchy (itchy) skin, and allergies. Allergies are common in people with atopic dermatitis and can be diagnosed with a skin test or a blood test. However, there is no specific test to diagnose atopic dermatitis.

A diagnosis of contact dermatitis suggests the presence of an eczema rash, which is usually accompanied by itching, and the ability to determine the trigger with the patch test.

A skin biopsy for atopic and contact dermatitis will show similar features, namely spongy changes in the epidermis, swelling of the epidermal cells of the skin that look like a sponge under the microscope. Therefore, a skin biopsy cannot distinguish between these two conditions.

Diagnosis of atopic dermatitis
Contact dermatitis diagnosis.

Watch out

Treatments for atopic and contact dermatitis are similar in order to reduce inflammation and itching and prevent future flare-ups.

Well-hydrated skin is recommended for both conditions, but is essential in atopic dermatitis. Regular use of creams or ointments can help reduce and prevent breakouts. Hydration can help soothe the skin during a flare-up of active contact dermatitis, but it will not prevent contact dermatitis.

Whether the eczema of the rash is due to atopic dermatitis or contact dermatitis, the main treatment is to identify and treat the cause.

The medications used to treat these conditions are also similar, but there are differences in when and how they are used.

  • Topical steroids : They are the mainstay of treatment for both atopic dermatitis and contact dermatitis, reducing inflammation, irritation, and itching. In mild cases, over-the-counter hydrocortisone is helpful; in others, prescription steroids may be required.
  • Oral steroids : These drugs can be used in cases of contact dermatitis when the rash is severe or generalized. Oral steroids are rarely used for atopic dermatitis.
  • Antihistamines : While they do not relieve the rash in either condition, oral antihistamines can help some people relieve itching.
  • Phototherapy : Phototherapy is sometimes used for adults with difficult-to-treat dermatitis.
  • Topical Calcineurin Inhibitors : Elidel (pimecrolimus) and Protopic (tacrolimus) are non-steroidal topical medications often used to treat atopic dermatitis in people 2 years of age or older. They are not used often for contact dermatitis, except in severe cases or those that have not responded to other treatments.
  • Diluted bleach baths – Recommended in certain cases to help reduce the amount of Staphylococcus aureus bacteria on the skin. Diluted bleach baths can help relieve atopic dermatitis, but are generally not recommended for contact dermatitis. The evidence for its effectiveness is mixed; A 2018 survey study found that chlorine baths improved symptoms of atopic dermatitis. A 2017 review found that whitening baths reduced the severity of atopic dermatitis, but plain water baths were just as effective.
Treatment of atopic dermatitis.

  • Regular hydration

  • Topical steroids

  • Phototherapy

  • Topical calcineurin inhibitors

  • Fine baths with bleach in some cases.

  • Oral steroids are rarely used.

Contact treatment for dermatitis.

  • Avoid triggers

  • Topical steroids

  • Phototherapy

  • Oral steroids for severe cases.

  • Topical calcineurin inhibitors are rarely used.

  • Diluted bleach baths are not used.

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