An Overview of Allergic Contact Dermatitis

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Allergic contact dermatitis is a delayed hypersensitivity skin reaction that occurs after you touch a substance that you are allergic to. Some common culprits include metals, latex, and personal care products, though there are several other possibilities. While not harmful, allergic contact dermatitis occurs in phases and usually results in a very itchy, red rash that may have scaling, cracking, blistering, and lichenification (thick, leathery skin patches).

Allergic contact dermatitis accounts for 20% of all contact dermatitis reactions.

Symptoms

The symptoms of allergic contact dermatitis include:

  • A raised, red rash
  • Intense itching
  • Blisters, which may ooze fluid (vesicles)
  • Dry, scaly patches
  • Areas of cracked skin (fissuring)
  • Swelling of the skin
  • Hives

The shape and location of the rash are important clues to the cause of the allergen. For example, the pattern of the rash caused by a reaction to metal will correspond exactly to the shape of the offending item, such as a watch or an earring.

Symptoms of allergic contact dermatitis can occur within a few hours of coming in contact with an offending substance, or they can arise up to several days later. Symptoms may persist for several weeks, even after the substance has been removed.

Lichenification can occur in chronic cases of contact dermatitis. Lichenified skin looks thick and leathery. The patches are dry and darker than the surrounding skin. Lichenification develops when an area of skin is repeatedly scratched over a long period of time.

Causes

Like any allergy, one that gives rise to allergic contact dermatitis is due to the immune system treating a harmless substance as something it needs to defend against. Just as you may sneeze if you are allergic to pollen and smell some flowers, you may break out in an allergic contact dermatitis rash if you are allergic to, say, preservatives and use cosmetics made with them.

Some of the more common substances that trigger allergic contact dermatitis include:

  • Metal, especially nickel and chromium: These metals are found in many costume jewelry pieces, belt buckles, and clothing closures (including the backs of buttons on jeans).
  • Rubber or latex found in items like gloves, condoms, balloons, and shoes.
  • Fragrance in cosmetic products: This includes fragranced soaps, perfumes, shampoos, and lotions.
  • Preservatives used in cosmetic products: Common offenders include parabens, quaternium-15, DMDM hydantoin, formaldehyde, and isothiazolinones.
  • Sunscreen products: The active ingredient oxybenzone, found in many sunscreens, is a common cause of photoallergic contact dermatitis (i.e., an allergic skin reaction that occurs only after you are exposed to both an allergen and the sun).
  • Poisonous plants, such as poison ivy, poison oak, and poison sumac
  • Adhesives: For example, those used in non-stick bandages and medical adhesive tape, glue used to apply false eyelashes, or tape used to for wigs.
  • Topical medications: Both topical over-the-counter and prescription medications can trigger reactions. Triple-antibiotic ointments (like Neosporin) are often problematic.
  • Balsam of Peru: A common ingredient in cosmetics, as well as food and drinks.

A skin reaction to something that you are not actually allergic to is called irritant contact dermatitis. With this type, there is no immune response to the substance, unlike with allergic contact dermatitis.

Phases

Allergic contact dermatitis has two distinct phases: the sensitization phase and the elicitation phase. The sensitization phase is when the skin first comes in contact with the offending substance. The elicitation phase is when the symptoms appear.

Sensitization Phase

During this phase, an antigen comes in contact with the skin. Because most of the antigens that cause this type of reaction have a low molecular weight, they can easily penetrate the outer layer of the properly functioning epidermis.

The antigen is processed by cells in the basal layer of the epidermis and then presented to white blood cells called T lymphocytes. These T lymphocytes recognize the antigen as foreign and circulate through the bloodstream back to the epidermis.

Elicitation Phase

The elicitation phase occurs in sensitized people who are re-exposed to the antigen. The T lymphocytes in the epidermis once again recognize the antigen as foreign, this time producing inflammatory chemicals designed to eradicate the antigen.

It is these chemicals that produce the characteristic skin rash.

Diagnosis

Your doctor will examine your rash and, if they suspect contact dermatitis, will ask for a detailed history. Your doctor may ask about your job, your hobbies, and your home life to help determine which substances may be triggering your rash, if any.

Patch testing is often done to identify allergens. This is a simple procedure in which small amounts of common allergens are placed on your back with an adhesive sheet. After 48 hours the patches are removed and the skin checked for allergic reaction. Another reading of the skin is done approximately two days later.

Patch testing is painless, although you may have some itching or irritation if you have a positive reaction to any of the patches. Knowing your potential triggers will help you can avoid these substances going forward.

It can be difficult to tell allergic contact dermatitis from other types, such as irritant dermatitis or atopic dermatitis (eczema), as the rashes they produce are similar. It's best to seek a professional opinion if you experience a rash so that you can get a proper diagnosis and the correct treatment.

Treatment

The mainstay of treatment for allergic contact dermatitis is avoiding the offending allergen (if one can be determined).

Over-the-counter (OTC) hydrocortisone creams can be used if your rash is mild or covers a small area. Apply up to four times per day, or as directed on the product packaging, and rub in gently but completely. Don't use OTC hydrocortisone on babies or young children without first talking to a pediatrician.

Topical steroids may be needed. These will help reduce inflammation and itching. When used as directed, these are very safe and effective treatments.

Oral steroids, such as prednisone, may be prescribed in very severe cases, or where the rash covers large areas of the body.

Other helpful measures to consider, especially if the allergen cannot be identified, include:

  • Minimize the topical products you're using: This reduces your exposure to potential allergens and allows the skin to heal. You may want to use plain water rather than soap and avoid make-up and perfumes altogether.
  • Use ointments instead of creams: Ointments, such as Eucerin or Aquafor, form an occlusive barrier over the skin that can ease discomfort.
  • Avoid botanical extracts found in "fragrance-free" or "natural" products, as these can be very allergenic. Also, some home remedies (e.g., herbal poultices, essential oils) may exacerbate inflammation, so use them only with your doctor's OK.
  • Be on the lookout for hidden allergens: For example, earring posts may be made of sterling silver or gold, while the backs are made of nickel.

A Word From Verywell

Allergic contact dermatitis is a common problem. While it's harmless, it can be uncomfortable enough to affect your daily life (and especially your ability to sleep). It may or may not be immediately clear what has triggered your rash, so work with your doctor to identify your triggers so you can do your best to avoid them. Patch testing, plus a bit of detective work, can help.

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  1. Zukiewicz-Sobczak WA, Adamczuk P, Wróblewska P, et al. Allergy to selected cosmetic ingredients. Postepy Dermatol Alergol. 2013 Oct;30(5):307-10. doi:10.5114/pdia.2013.38360


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