The Differences Between Atopic and Contact Dermatitis

Woman scratching contact dermatitis on her neck

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In many instances, the difference between atopic dermatitis and contact dermatitis is quite obvious. In other cases, not so obvious. Some patients can even have both atopic and contact dermatitis at the same time, which is even more difficult to assess. While there are many similarities between these two common conditions, there are some important differences especially when it comes to the causes of dermatitis.

Atopic vs. contact dermatitis
Verywell / JR Bee

Symptoms

Both atopic and contact dermatitis are forms of eczema. There are generally three different phases of eczema:

  1. Acute eczema is characterized by itchy blisters (vesicles) on inflamed, red skin.
  2. Sub-acute eczema is an itchy, dry, flaky, crusting, or oozing of the skin.
  3. Chronic eczema is characterized by lichenification, a leathery thickening of the skin that occurs as a result of chronic scratching.

Eczema is not a diagnosis. Rather, eczema refers to the actual rash that occurs as a result of these conditions.

Therefore, atopic dermatitis and contact dermatitis in many cases look identical. Because of this, it can be difficult to differentiate between the two just based on symptoms alone.

Both types of dermatitis cause a red, itchy rash. While these symptoms can apply to each, atopic dermatitis is more likely to be dry and scaly while contact dermatitis is more likely to blister and weep. Both conditions cause itching, but contact dermatitis also causes pain and burning.

Age

The age of a person experiencing atopic dermatitis is an important distinction between these two conditions. Most people developing atopic dermatitis are five years of age or younger, while contact dermatitis is less common in young children.

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

Location

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

Atopic dermatitis most classically involves the flexural locations of the skin, such as the folds of the elbows (antecubital fossa), behind the knees (popliteal fossa), the front of the neck, folds of the wrists, ankles, and behind the ears.

The flexural areas are most often involved in older children and adults because these areas are easiest to scratch. Since atopic dermatitis begins as an itch that, when scratched, results in a rash, it makes sense that the locations easiest to scratch will be the areas that develop a rash.

On the other hand, contact dermatitis occurs at the site of chemical exposure, and therefore can virtually be anywhere on the body. These are often areas that aren't typically affected by atopic dermatitis, for example, on the stomach (due to nickel snaps on pants), under the arms (from antiperspirants), and the hands (from wearing latex gloves).

Atopic Dermatitis Symptoms

  • Often dry and scaly

  • Appears on flexural areas

  • Most common in children under 5 years old

Contact Dermatitis Symptoms

  • Often blisters and weeps

  • Can appear anywhere on the body

  • Most common in adults

Causes

There are many important differences between atopic and contact dermatitis, with the most important being the susceptibility of a person to develop the condition.

Atopic Dermatitis Mechanism

A person with atopic dermatitis often has a genetic mutation in a protein in their skin called filaggrin. A mutation in filaggrin results in a breakdown of the barriers between epidermal skin cells.

This leads to dehydration of the skin as well as the ability for aeroallergens, like pet dander and dust mites, to penetrate the skin. Such aeroallergens result in allergic inflammation and a strong itching sensation. Scratching further disrupts the skin and causes more inflammation and more itching.

An underlying propensity for allergy can also cause eczema to develop as a result of eating a food to which a person is allergic, causing T-lymphocytes (a type of white blood cell) to migrate to the skin and result in allergic inflammation. Without these underlying propensities, a person is unlikely to develop atopic dermatitis.

Contact Dermatitis Mechanism

Contact dermatitis, on the other hand, is due to a reaction to a chemical exposure directly on the skin. It occurs among a majority of the population from interaction with poison oak (approximately 90%) and is also common when exposed to nickel, cosmetic agents, and hair dye.

A person still must have the ability of their T-lymphocytes to recognize a chemical as a foreign substance and react to it in order to develop contact dermatitis.

Atopic Dermatitis Causes

  • Genetic susceptibility

  • Common in those with allergies and asthma

  • Triggers include stress, skin irritation, and dry skin

Contact Dermatitis Causes

  • Topical exposure to offending substance

  • Delayed hypersensitivity response

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

Diagnosis

Both atopic dermatitis and contact dermatitis are diagnosed primarily by visual inspection of the rash along with a thorough medical history. Age of the person affected and the location of the rash are used to help differentiate between the two conditions.

The diagnosis of atopic dermatitis involves the presence of eczema, the presence of itching (pruritus), and the presence of allergies. Allergies are common in those with atopic dermatitis and can be diagnosed using skin testing or blood testing. There is no specific test to diagnose atopic dermatitis, though.

The diagnosis of contact dermatitis involves the presence of eczema, which is usually itchy, and the ability to determine the trigger with the use of patch testing. Contact dermatitis isn’t caused by an allergic process, but as a result of T-lymphocyte mediated delayed-type hypersensitivity.

A skin biopsy of both atopic and contact dermatitis will show similar features—namely spongiotic changes of the epidermis, a swelling of the epidermal skin cells that appear like a sponge under a microscope. Therefore, a skin biopsy will not differentiate between these two conditions.

Diagnosing Atopic Dermatitis

  • Itchy rash with typical age and location patterns

  • Family history

  • Allergies diagnosed by blood test and patch test

Diagnosing Contact Dermatitis

  • Itchy rash

  • Identifying contact with triggers

  • Patch testing

Treatment

Treatment for both atopic and contact dermatitis is similar, with the goal of reducing inflammation and itching, and preventing future breakouts.

Keep the skin well-moisturized is recommended for both conditions, but it's critical for atopic dermatitis. Regular application of creams or ointments helps reduce and can prevent a flare of atopic dermatitis. Moisturization can help soothe the skin during an active contact dermatitis flareup but it will not prevent contact dermatitis

Regardless of the eczema is from atopic dermatitis or contact dermatitis, identifying and ​avoiding the cause is the main treatment modality.

Medications used to treat the conditions are similar as well, but there are differences in when and how they're used.

  • Topical steroids: A mainstay of treatment for both atopic dermatitis and contact dermatitis, these medications reduce inflammation, irritation, and itching. Over-the-counter hydrocortisone is helpful for mild cases, while prescription steroids may be needed in others.
  • Oral steroids: The may be used in cases of contact dermatitis where the rash is severe or widespread. They are rarely used for atopic dermatitis.
  • Antihistamines: Although they don't clear up the rash in either condition, oral antihistamines can help relieve itching for some people.
  • Dilute bleach baths: These are recommended in certain cases to help reduce Staphylococcus aureus bacteria on the skin. Dilute bleach baths may help improve atopic dermatitis but are generally not recommended for contact dermatitis.
  • Topical calcineurin inhibitors: Elidel (pimecrolimus) and Protopic (tacrolimus) are non-steroid topical medications often used to treat atopic dermatitis in those ages 2 and older. They aren't often used for contact dermatitis except in severe cases or those that haven't responded to other treatments.

Atopic Dermatitis Treatment

  • Regular moisturization

  • Topical steroids

  • Oral steroids rarely used

  • Topical calcineurin inhibitors

  • Dilute bleach baths in some cases

Contact Dermatitis Treatment

  • Avoiding triggers

  • Topical steroids

  • Oral steroids in severe cases

  • Topical calcineurin inhibitors rarely used

  • Dilute bleach baths not used

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