What to know: Atopic dermatitis vs. contact dermatitis

Atopic dermatitis (AD) is the most common type of eczema, which is why some people simply refer to it as eczema. It causes people’s skin to become discolored, itchy, cracked, and dry.

It is a chronic skin condition that comes and goes throughout an individual’s life. Eczema runs in families and often occurs in people with a family or personal history of asthma and hay fever. AD usually begins in childhood, affecting 15–20% of children, and may continue to affect 1–3% of the adult population worldwide.

Contact dermatitis (CD) is also a skin condition where a person develops skin redness, inflammation, and other lesions after coming into contact with an irritant or allergen that triggers an allergic reaction. It is also fairly common, accounting for 70–90% of all work-related skins conditions.

There are two types of contact dermatitis: allergic (ACD) and irritant contact dermatitis (ICD). ACD refers to a person experiencing an allergic reaction following skin contact with an allergen, while ICD results from an external factor that damages a person’s skin.

There are several differences between AD and CD. These include:

Cause

AD is a chronic condition due to a combination of hereditary, immune, and environmental factors. While most children can grow out of it, some of them will experience flare-ups throughout their lives.

In contrast, CD is not normally hereditary nor a chronic condition — it does not usually relate to other allergic conditions, such as hay fever or asthma. However, some people with atopic tendencies may be more susceptible to CD.

In CD, skin reactions only occur upon exposure to an irritant or allergen. A person’s skin condition usually improves or clears upon the identification, removal, and avoidance of the cause.

Age

AD usually presents early in life, affecting around 60% of children during their first year. On the other hand, all individuals are at risk of developing CD, but it occurs more in adults than children.

Cell involvement

In AD, allergens and infections trigger higher immunoglobulin E (IgE) antibody levels in the person’s blood. In contrast, while there is also an immune system involvement in ACD, it is due to a type of immune cell called sensitized T-cells. In ICD, the reaction occurs following the release of pro-inflammatory cytokines in response to the irritant.

Both conditions present with skin lesions, making it difficult to differentiate the two based on the type of rashes alone.

However, the location of the rashes may help differentiate the two conditions. AD lesions have a typical distribution based on age. In infants and toddlers, the rash typically appears on the face and extensor surfaces, such as the back of their elbows and feet. In children and adolescents, it usually occurs in flexural areas, such as the back of their knees, front of the elbows, front of the ankles, and the skin creases in the neck.

In contrast, CD rashes can occur on any part of a person’s body that encounters an irritant or allergen. However, lesions often affect a person’s face, hands, and neck. Skin lesions in CD, especially in the irritant type, often have visible borders.

According to the National Eczema Association, a person may have both AD and CD. This is because they have different triggers.

A 2019 study mentions a multifaceted relationship between the two conditions, and a 2018 article adds that ICD can co-exist with both AD and ACD. Additionally, a 2018 review suggests that people with AD have abnormal immune system processes, disrupted skin barriers, and frequently use topical medications and emollients, predisposing them to develop ACD.

Evidence suggests an association between AD and a mutation in the FLG gene, which produces a protein called filaggrin. This protein plays a role in skin hydration, and research suggests that a shortage of filaggrin can impair the skin’s barrier function, which may contribute to the development of AD.

Exposure to environmental triggers, such as changes in temperature, skin irritants, and allergens, may also cause flare-ups in people with AD. In CD, people develop skin lesions after exposure to an irritant or allergen. Many different allergens can trigger both types of dermatitis. Examples include:

AC and CD have similar symptoms, and both typically undergo the 3 stages of eczema: acute, subacute, and chronic. Both conditions present with discoloration, itching, and skin lesions such as cracked weeping skin, plaques, and small blisters in the acute phase. While both are itchy, CD is more likely to result in stinging, burning, and painful sensations.

Both conditions may present with thickened, leathery skin in the chronic phase. The person’s skin may also have cracks, fissures, and color changes.

A doctor diagnoses a person with AD based on the condition’s persistent history, the skin lesion’s features, appearance, distribution, and other associated signs. According to the American Academy of Dermatology, essential features should be present. These include:

• itching
• typical appearance and age-specific patterns
• chronic or relapsing history

A family or personal history of atopy, having the disorder at a young age, and dry skin are symptoms present in most cases and support a person’s AD diagnosis.

A health practitioner can typically diagnose CD following a physical examination and the appearance of the skin. To help identify the allergen or irritant, they will ask about a person’s family history, occupation, lifestyle, and medication use. They may also suggest a patch test to check a person’s reaction against known allergens.

The goal for both conditions are similar — management involves avoiding triggers and irritants. However, management for CD is more straightforward than AD. Since AD is lifelong, doctors usually create an individualized plan to manage a person’s condition.

Over-the-counter products, such as antihistamines, pain relievers, or topical hydrocortisone, can help relieve mild symptoms. Doctors may also prescribe topical medications to treat small areas. However, if the skin lesion is severe or covers a large area, doctors may prescribe a short course of oral medications.

Other treatments for AD may include:

• proper bathing and moisturizing
• wet wraps
• biologic drugs
• immunosuppressants
• phototherapy
• complementary therapies, such as meditation or yoga

Skin lesions from CD usually clear up and do not usually become a cause for concern. However, individuals should see their doctors if their rashes do not go away, become widespread, or become very uncomfortable or painful.

Similarly, people with AD should check with their doctors if:

• symptoms worsen
• it disturbs their sleep and daily activities
• the time between flare-ups shortens
• new lesions appear or affect new areas

Atopic dermatitis and contact dermatitis are two common types of eczema that are often confused. While they are both inflammatory skin conditions that share similar symptoms, their causes are different. Atopic dermatitis is an internal skin condition, whereas contact dermatitis results from external factors.

Proper diagnosis is important to ensure that individuals receive the appropriate treatment to help clear the skin and manage the condition.