The term “dermatitis” refers to any skin inflammation. Contact dermatitis refers to an inflammatory reaction of the skin that is elicited upon skin contact with a specific substance. The inflammatory skin reaction is characterized by a localized dilation of the subcutaneous blood vessels that leads to increased blood flow in the area.
Fluid from the blood also leaks out into the subcutaneous tissue spaces as the blood vessels become more leaky. This causes the overlying skin area to appear red and swollen. The inflamed skin area is also warm to the touch and can be itchy or painful. Prolonged inflammation can cause the affected skin area to dry up and become scaly.
There are a variety of substances that can cause skin inflammation upon coming in contact with the skin. Some of these substances can cause skin inflammation in any person upon prolonged contact. Such an inflammatory skin reaction is known as irritant contact dermatitis.
In other cases, contact with a specific substance elicits an inflammatory skin reaction only in certain hypersensitive individuals. This type of contact dermatitis is known as an allergic contact dermatitis. Despite the similar appearance of skin reactions, the triggers and mechanisms of irritant contact dermatitis and allergic contact dermatitis are different.
What is allergic contact dermatitis?
Allergic contact dermatitis does not occur in every person. Only certain hypersensitive individuals are prone to allergic contact dermatitis when they come in repeated physical contact with a specific substance. Unlike irritant contact dermatitis, allergic contact dermatitis involves an abnormal immune response towards the offending substance (also referred to as the allergen). A variety of allergens can trigger the immune response in susceptible individuals leading to skin inflammation at the site of contact.
Allergic contact dermatitis is similar to another type of allergic dermatitis known as eczema or atopic dermatitis. However, these two are different conditions and should not be confused with each other. Atopic dermatitis is most commonly seen in young children. Also, individuals who already have atopic dermatitis are more likely to be prone to allergic contact dermatitis as well.
Read more about irritant contact dermatitis.
How does allergic contact dermatitis occur?
The inflammatory immune response in allergic contact dermatitis does not occur upon first contact with the allergen. A susceptible individual first develops a sensitivity to the allergen upon initial contact with it. This sensitization process usually takes about 10-14 days after the first exposure to the allergen. However, in some individuals, the sensitization may take years of continuous exposure to an allergen.
Once sensitized, a susceptible person will react to any subsequent exposure to the same allergen with an inflammatory reaction. This allergic reaction may occur within a few minutes or hours after exposure to the allergen. However, in some people the allergic reaction may take a few days to develop.
Due to the gap between the first exposure to an allergen and the development of an allergic reaction towards it, allergic contact dermatitis is also referred to as a delayed hypersensitivity reaction (type IV cell-mediated hypersensitivity reaction). The following events occur in the body during the first and subsequent exposures to the allergen:
- Initial exposure to an allergen: The first exposure to the allergen triggers the sensitization process in a susceptible individual. The allergens are trapped by a certain type of immune cells (known as Langerhans cells) present within the epidermal layer of the skin. The Langerhans cells then migrate to a nearby lymph node in the region, where they expose the allergen to another type of immune cell known as the T-cell. After sensitization, the T-cells travel to the epidermis.
- Subsequent exposure to the same allergen: Any subsequent exposure to the allergen will activate the sensitized T-cells present in the epidermis. Activated T-cells release cytokines that recruit inflammatory cells into the region and the inflammatory reaction begins.
Signs and Symptoms
The signs and symptoms of both allergic contact dermatitis and irritant contact dermatitis are very similar. Individuals affected with both these conditions usually present with the following signs and symptoms:
- A red skin rash is usually present. The rash may have blisters (tiny or large) or ulcers.
- The affected skin area may become dry. The dry skin may also peel off.
- The affected skin area may be intensely itchy.
- Pain may be present, especially when the skin is peeling off or is infected.
- Scratching of the affected skin area may lead to breaks in the skin, which makes the skin prone to secondary bacterial infections. Infected skin areas may lead to additional signs and symptoms such as pain, pus, and fever.
These signs and symptoms are usually localized, but may spread to other parts of the body. The skin on the hands are most commonly affected in both allergic contact dermatitis and irritant contact dermatitis. This is because the hands are most likely to come in contact with an allergen or irritant as we manipulate things in our environment. The skin on the face, neck, and scalp are also frequently affected in allergic contact dermatitis.
Causes of Allergic Contact Dermatitis
Allergic contact dermatitis can be elicited by a variety of allergens. The following are some of the substances that are commonly found to trigger the inflammatory reaction of allergic contact dermatitis.
Exposure to certain metals can cause both irritant contact dermatitis and allergic contact dermatitis. Cobalt, nickel, and mercury are some common metals that people get exposed to in a variety of occupational settings. In fact, nickel is one of the most common cause of allergic contact dermatitis. Metals present in jewelry may also cause allergic contact dermatitis in some individuals.
Allergic contact dermatitis due to hair dyes usually affects the skin on the scalp, face and neck. The main allergen in hair dyes that is responsible for most cases of allergic contact dermatitis is para-phenylenediamine (commonly abbreviated as PPD). Dyes like henna can also cause allergic contact dermatitis in other regions of the body.
Some plants contain chemicals that frequently act as allergens. Examples include primrose, poison ivy, oak, ragweed pollen, and sumac.
Topical medications such as antihistamines, antibiotics, NSAIDs, corticosteroids, neomycin, and benzocaine can cause allergic contact dermatitis. Some of these topical medications become allergens only upon exposure to sunlight.
Chemicals contained in commonly used cosmetics such as nail polishes, waxes, deodorants, hair removal creams, and foundation creams can also trigger allergic contact dermatitis in susceptible individuals.
Allergic contact dermatitis can also occur upon contact with deodorants, colognes, air fresheners, perfumes, and detergents.
Some people are allergic to latex contained in gloves, condoms, and catheters.
Chemicals used in manufacturing industries (such as shoe and textile industries) can also cause allergic contact dermatitis.
Treatment for Allergic Contact Dermatitis
Identifying the responsible allergen and avoiding contact with it is the main line of defense against allergic contact dermatitis. Treatment of allergic contact dermatitis includes the following:
- Oral antihistamines may be prescribed to reduce any itching sensations.
- Corticosteroids are commonly used to treat allergic contact dermatitis. Topical immunomodulators may be used if corticosteroids fail to provide relief.
- A dry skin may require the use of emollients.
- One may use cold water compress on the affected skin areas to provide relief.
- Psoralen and ultraviolet light A (commonly abbreviated as PUVA) treatment may be given in chronic cases of allergic contact dermatitis.
- In severe cases of allergic contact dermatitis, immunosuppressants may be used.