Normally, you can easily tell the difference between atopic dermatitis and contact dermatitis. However, in some cases it is not so obvious. It is also possible that both conditions occur at the same time, which makes it even more difficult to diagnose the correct disease.
Although atopic dermatitis and contact dermatitis may be quite similar in certain aspects, they also have a number of significant differences.
Similarities Between the Conditions
One of the main similarities between atopic and contact dermatitis is that they both cause rash, or eczema. Although the term eczema is more commonly associated with atopic dermatitis, it actually can be used to describe any skin condition causing rash, including contact dermatitis. Experts determine three different phases of eczema: acute eczema, sub-acute eczema and chronic eczema.
Acute eczema is a condition characterized by inflamed skin with itchy blisters. Sub-acute eczema symptoms include a dry, itchy, flaky, crusting, or oozing of the skin. Chronic eczema implies lichenification – leathery thickening of the skin caused by chronic scratching.
A biopsy of the skin is unlikely to help make a correct diagnosis. Both diseases look similar under a microscope – swelling of epidermal skin cells visually reminding a sponge, which is why a biopsy will not be able to differentiate between the two.
Differences Between the Conditions
The most significant distinction between atopic dermatitis and contact dermatitis lies in a patient’s susceptibility to developing the disease.
Atopic dermatitis often implies a presence of a genetic mutation in filaggrin – a protein in the skin. This mutation causes the barriers between the epidermal skin cells to break down, leading to dehydration of the skin and letting various aeroallergens, such as pet dander or dust mites, affect the skin.
Penetration of the allergens into the skin is followed by an allergic inflammation and strong itchiness of the skin. Scratching the skin is not recommended, as it leads to more inflammation and stronger itchiness.
In people, susceptible to developing an allergy, eczema may occur after eating a food they are allergic to. This causes migration of T-lymphocytes to the skin, resulting in allergic inflammation. People without an underlying propensity for allergy are unlikely to experience atopic dermatitis.
Unlike atopic dermatitis, contact dermatitis occurs as a result of the skin’s reaction to a direct chemical exposure. The most common contact dermatitis trigger is poison oak whose exposure on the skin leads to an allergic reaction in approximately 90 percent of population. Other chemicals causing contact dermatitis include nickel, cosmetic products, and hair dye.
Contact dermatitis occurs in people, whose T-lymphocytes recognize a chemical as a foreign substance, and therefore, react to it.
Another significant difference between atopic dermatitis and contact dermatitis is the age of a person that develops a condition. While contact dermatitis can occur at any age, atopic dermatitis mostly affects infants and young children.
Besides, the distinction between the conditions can be told based on the location of the rash caused by them.
Atopic dermatitis, eczema, appears in the areas of the skin where a person scratches, while contact dermatitis can occur anywhere throughout the body, depending where the skin was exposed to a chemical.
Common locations of the skin affected by atopic dermatitis include mostly flexural locations, such as the outer side of the elbows, behind the knees, front side of the neck, behind the ears, wrist folds, and ankles, since these areas are easy to scratch.
Making a Diagnosis
Since atopic dermatitis is an allergic rash, a person can be diagnosed with this condition, if such symptoms as eczema and itching are present, and the person is susceptible to allergies. The presence of allergies can be determined with a help of skin tests and blood tests.
Unlike atopic dermatitis, contact dermatitis is not caused by an allergy. It results from the condition known as T-lymphocyte mediated delayed-type hypersensitivity. The diagnosis of contact dermatitis can be made, if a patient experiences eczema, usually itchy, and it is possible to identify the trigger by conducting patch tests.