Allergic contact dermatitis is one of two forms of contact dermatitis, in which skin contact with a particular substance triggers an allergic skin reaction. The other form is irritant contact dermatitis (ICD), which is more common than ACD and has slightly differing clinical features. ACD presents with symptoms similar to those of eczema with skin typically becoming very dry, scaly and itchy.

Causes of allergic contact dermatitis

The allergic reactions seen with ACD are triggered by protein molecules (allergens) present in a particular substance. Immune cells within the skin mount an immune attack that leads to symptoms of allergy. Some of the materials that commonly trigger the allergic reaction include nickel, cobalt, cosmetics, perfumes, hair dyes, medicine preservatives and latex in rubber.

In the case of ICD, substances physically break the skin and expose cutaneous skin cells to the allergen. Examples of irritants include detergents, cosmetics, soaps, perfumes, solvents, oils, chemicals, dust and plants.

Symptoms of ACD

Although the clinical presentation of ACD and ICD is similar, there are some small differences in symptoms which help distinguish between the two:

• With ACD, the main symptom is similar to that seen with eczema - a very dry, scaly and itchy skin, whereas with ICD sore, burning and stinging skin is typical.
• ICD only affects local areas of the skin that have come directly into contact with an allergen, while with ACD the rash may be more widespread and affect other areas.
• ACD may manifest anything from hours to days after contact with the allergen, while the onset of ICD usually occurs within 48 hours.
• ACD may take many days to resolve while with ICD symptoms are usually allayed within four days.

Diagnosis and treatment

Diagnosis is based on a clinical history of reactions to potential allergens after exposure. For confirmation of diagnosis, a skin prick test and allergen specific IgE tests are usually used.

Avoidance of the allergen potentially leading to an allergic reaction is the most common approach to preventing ACD. In addition, the following measures may be taken:

• Use of skin moisturizers and emollients to soothe the skin and prevent it from drying and cracking
• Use of corticosteroid creams to reduce the allergic inflammatory symptoms
• Use of antihistamine medications to reduce itching and allergic manifestations
• If an affected area acquires a secondary bacterial infection, both locally applied and oral antibiotics may be used alone or in combination