Contact Dermatitis, Patch Testing, and Allergen Avoidance

Abstract

In patients presenting with a complaint of rash, contact dermatitis is often the underlying diagnosis making it an entity with which health care providers should be familiar. Contact dermatitis can be divided into irritant contact dermatitis and allergic contact dermatitis. In a patient suspected of having allergic contact dermatitis, patch testing can be done to identify specific allergens. Education focused on allergen avoidance and safe products is an integral part of treatment for the contact dermatitis patient. Knowledge of the most common allergens is helpful for clinicians to be able to provide this education.

What Is Contact Dermatitis?

Contact dermatitis is inflammation of the skin induced by chemicals when they come in contact with the skin. In the acute phase contact dermatitis has the appearance of erythema, vesiculation (blister formation), weeping, and crusting (See Figure 1). In the chronic phase contact dermatitis demonstrates scaling, fissuring (cracking), and lichenification (accentuated skin lines) (See Figure 2). There are four general categories of contact dermatitis including irritant contact dermatitis, allergic contact dermatitis, photocontact dermatitis, and contact urticaria. The vast majority of contact dermatitis falls into the first two categories of irritant or allergic contact dermatitis.

Figure 1.

Acute contact dermatitis to poison ivy demonstrating erythema, vesiculation and crusting.

Figure 2.

Chronic contact dermatitis to a preservative in shampoo demonstrating scaling and lichenification.

Irritant Contact Dermatitis

Irritant contact dermatitis accounts for approximately 80 percent of contact dermatitis. It is a non-immunologic form of contact dermatitis meaning it causes damage to the skin without prior sensitization of the immune system. Irritant contact dermatitis can occur in any member of the population; however, there is variation in individual susceptibility with those in high-risk occupations being the most susceptible. High-risk occupations include caterers, furniture industry workers, hospital employees, hairdressers, chemical industry workers, dry cleaners, metal workers, and florists. The mechanism by which irritant contact dermatitis causes inflammation of the skin is through denaturation of epidermal keratins, removal of skin surface lipids, damage to cell membranes and direct cytotoxic effects. Irritant contact dermatitis is usually caused by the chronic effect of exposure to a weak irritant. The most common causative agents are solvents such as alcohol, xylene, turpentine, acetone and ketones; metalworking fluids; surfactants such as sodium lauryl sulfate; alkalis in soap; and acids. Hands are the most commonly affected area in irritant contact dermatitis.

Allergic Contact Dermatitis

Allergic contact dermatitis makes up most of the remaining 20 percent of contact dermatitis. It is a type IV delayed hypersensitivity reaction which requires prior sensitization with a genetic predisposition. Allergens are usually of low molecular weight and are lipid soluble which allows them to penetrate the skin barrier. There are two phases to a type IV hypersensitivity reaction: the sensitization phase and the elicitation phase.¹ The sensitization phase starts with an unprocessed antigen, called a hapten, penetrating the skin barrier and being taken up by an antigen-presenting cell, typically the epidermal Langerhans’ cell. As the Langerhans’ cell migrates to the draining lymph node the hapten is chemically altered within the cell and is conjugated with an HLA-DR molecule to form the complete antigen. The complete antigen is then expressed on the surface of the Langerhans’ cell and presented to CD4+ helper T-cells in the regional lymph nodes. The helper T-cells clonally expand and these memory T-cells migrate to the skin. The elicitation phase occurs when there is re-exposure to the allergen (hapten). It is again taken up by Langerhans’ cells and presented to the specific memory T-cells in the skin via HLA-DR.² Cytokines are produced including IL-1, IL-6 and GM-CSF leading to mast cell and macrophage activation with subsequent inflammation, cellular destruction and repair. After sensitization, skin inflammation develops 24 to 48 hours after re-exposure.

Patch Testing

Although clinicians may biopsy rashes to try and determine whether contact dermatitis is irritant or allergic in nature, there are no histologic features that have been shown to consistently favor one over the other.³ Instead, patch testing is used to produce in miniature an eczematous reaction by applying allergens under occlusion on intact skin of patients suspected of being allergic. The T.R.U.E. (Thin-layer Rapid-Use Epicutaneous) Test is a pre-made patch test that consists of 35 allergens incorporated into hydrophilic gels. The T.R.U.E. test is widely used by Dermatologists and Allergists due to its convenience and ease of use. The disadvantages of the T.R.U.E. test include the limited number and somewhat outdated nature of the allergens in the panel. Studies have shown that extended patch testing reveals 37–76 percent more positive reactions and 50% have positive reactions only to non-T.R.U.E. test allergens.^{4, 5} More extensive patch testing typically requires manual loading of allergens into wells which is more time and labor intensive as well as costly. Various allergen panels are available; the North American Contact Dermatitis Group standard series of 65 allergens is one such panel.

Regardless of the panel used, allergens are affixed to intact skin on the patient’s back (See Figure 3). After occlusion for 48 hours (day 3) the patches are removed for the first reading. The patient then returns in another 48 hours (day 5) for the final reading. Patients must avoid showers, wetting the site, ultraviolet irradiation, and excessive sweating for the entire five days of patch testing. In addition, patients cannot use topical steroids on the back until after the final reading. Positive reactions are scored in the following way: ?/+: doubtful (macular erythema), +: weak (papular erythema), ++: strong (edematous or vesicular), +++: extreme (bullous or ulcerative). True allergic reactions should persist or appear at the day 5 reading.

Figure 3.

Allergen panels being placed on the back of a patient undergoing patch testing.

Allergen Avoidance

The most crucial part of patch testing is the patient education that occurs once the final reading has taken place. It is important to provide the patient with written information on all of the allergens with a positive reaction. This written information should include the allergen name, synonyms, typical uses, and strategies on ways to avoid the chemical. The American Contact Dermatitis Society’s (ACDS) website (www.contactderm.org) provides helpful handouts for many of the more common allergens. These handouts are available to members of the Society. Another resource available to members of the ACDS is the Contact Allergen Management Program (C.A.M.P.). This database provides a list of products that are safe for a patient to use once the patient’s allergens have been entered into the system--in essence, the patient’s “shopping list.”

When reviewing allergens with the patient it is important to try to determine relevance of each allergen to the patient’s dermatitis. An allergen is clinically relevant if there is existence of an exposure and the patient’s dermatitis is explainable (totally or partially) with regard to that exposure. Strategies to help establish relevance include taking a comprehensive clinical history especially as it relates to occupational or non-occupational exposures. Examples of non-occupational exposures include skin care products, hobbies, and jewelry. Another strategy to establish relevance is an environmental evaluation with research into the composition of products to which the patient has been exposed. This information may come from ingredient lists, Material Safety Data Sheets (MSDS) and manufacturers.

It is helpful to know the most common allergens based on current patch test data in an effort to provide some proactive counseling even prior to formal patch testing. Following are the most common allergens detected in patients undergoing patch testing as identified by the North American Contact Dermatitis Group (NACDG) from 2011–2012 and published in the journal Dermatitis in 2015.⁶

Metals (Nickel and Cobalt)

Nickel sulfate is the most common allergen with 18.5% of patients that are patch tested having a positive reaction. This high rate of sensitivity is attributed to the common practice of ear and body piercing. Nickel dermatitis can present as earring dermatitis, dermatitis under a necklace or watch back (or more recently a Fitbit®.)⁷ Dermatitis of the mid-abdomen can be caused by nickel in a belt buckle or snap. Sweating can increase the amount of metal leached from a product. The dimethylglyoxime test can detect the presence of nickel in metal objects for a patient suspected of or proven to have nickel allergy. In order to avoid nickel, patients should be counseled to look for high-quality stainless steel, copper, sterling silver, yellow or rose gold of at least 12 carats (white gold actually does contain nickel), platinum, aluminum, brass and titanium.

Cobalt is a metal used for its hardness and often combined with other metals. Because of this, 80 percent of patients allergic to cobalt are also found to be allergic to chrome and/or nickel.⁸

Fragrance (Balsam of Peru, Fragrance Mix I, Fragrance Mix II)

Fragrance allergy can be detected using a variety of allergens. Balsam of Peru is a common screening fragrance; however it only detects approximately 50% of fragrance-allergic patients. It is the resin of the Myroxylon pereirae tree native to Central America and is used as a fragrance or preservative in a variety of personal use products. Fragrance mix I and II are more complete allergens used to detect fragrance allergy in patch test patients. Although not as prevalent as nickel allergy, (7.9% for Balsam of Peru, 12.1% for fragrance mix I and 5.2% for fragrance mix II) allergy to fragrance is found to be relevant to the patient’s dermatitis a staggering 87 percent of the time. It is important for patients with fragrance allergy to use “fragrance-free” products rather than “unscented” products since “unscented” products may actually contain masking fragrance to cover unpleasant odors!⁹

Topical antibiotics (Neomycin and Bacitracin)

Neomycin (positive in 9.1% of patch test patients) and bacitracin (positive in 7.8% of patients tested) are both topical antibiotic preparations found in common over-the-counter products such as Neosporin® Original (neomycin and bacitracin) and Polysporin® Original (bacitracin). Co-reactivity between these two allergens is common since they are often found in the same or similar products. Caution should be employed in patients with chronic leg ulcerations as these patients show a high degree of sensitization to these topical antibiotics. Bacitracin is especially dangerous because of the real, although low, risk of anaphylaxis with topical exposure. Neomycin and bacitracin can remain in fabric even after washing so it is best to discard any fabrics that were in contact with the antibiotic once allergy is discovered. Prescription topical antibiotic preparations, such as mupirocin are much less allergenic and can be used with patients in need of topical antibiotics. Of note, clean skin surgery procedures such as biopsies and excisions have a low rate of infection and topical antibiotics do not need to be used for wound care. Instead petrolatum ointment is adequate in this setting.¹⁰

Formaldehyde (and Quaternium-15)

Formaldehyde, positive in 6.6% of patch test patients, is used as a preservative in cosmetics, medications, textiles, paints, cigarette smoke, paper, and plastic bottles. Textile dermatitis can be caused by formaldehyde in wash-and-wear, permanent press or wrinkle-free clothes. Formaldehyde allergy in this setting can present as axillary dermatitis with sparing of the axillary vault since the fabric does not directly contact this area. One hundred percent polyester clothing contains the least amount of formaldehyde and washing clothing in one cup of powdered milk can remove excess formaldehyde; however, the formaldehyde will never be completely depleted. Formaldehyde-free undergarments can also be worn under clothing in an attempt to avoid this allergen.

Today, formaldehyde is rarely used in its pure form in personal use products; however a variety of formaldehyde-releasing preservatives are used in these items. Quaternium-15, positive in 6.5% of tested patients, is the most common cause of preservative-induced dermatitis and is found in products such as shampoo, moisturizer, conditioner, and soap. It is found to be relevant in 89 percent of patients allergic to it. There are non-formaldehyde-releasing preservatives used in personal use products and a safe product list proves to be extremely helpful for these patients.¹¹

Para-phenylenediamine

Para-phenylenediamine (PPD) is a black dye found in not only black, but also brown hair dyes. It can be relevant to both people that color their hair as well as hairdressers. PPD is also found in black henna tattoos, which can lead to sensitization and subsequent dermatitis with re-exposure. Bleach and PPD-free hair dyes (such as vegetable dyes or Elumen by Goldwell®) are alternatives for patients found to have PPD allergy.¹²

Recommended Products

In patients suspected of having contact allergy and in whom patch testing has not been performed, it can be helpful to recommend products that contain the least amount of potential allergens in an attempt to either improve the patient’s condition while they are awaiting Dermatology or Allergy consultation for patch testing or to completely resolve the patient’s dermatitis, thereby eliminating the need for patch testing altogether. “Safe” products in Table 1 was generated using the most common allergens found in personal use products taking into account the clinical relevance of each of those allergens.¹³

Table 1.

Safe Products Using the Most Common Allergens

Soap Aveeno® Active Naturals Moisturizing Bar CeraVe® Hydrating Cleanser

Hair Conditioner Cleure® Replenishing Conditioner DHS® Conditioning Rinse with Panthenol

Hair Shampoo Cleure® Volumizing Shampoo SLS Free Free & Clear® Shampoo for Sensitive Skin & Scalp

Moisturizer Aveeno® Eczema Therapy Moisturizing Cream CeraVe® Moisturizing Cream

Antiperspirant/Deodorant Speed Stick® Power Unscented Antiperspirant & Deodorant Solid

Sunscreen Neutrogena® Pure and free Baby faces Ultra Gentle Sunblock SPF 50

Laundry Detergent 7th Generation® Free & Clear Natural Laundry Detergent Ultra Tide® Free Powdered Detergent

Conclusion

Contact dermatitis is often the underlying diagnosis in patients presenting with complaint of rash. Most contact dermatitis is irritant in nature and recommending avoidance of irritating substances as well as dry skin care measures with gentle skin cleansers and regular moisturizer use can control most of these patients’ dermatitis. However, in about 20 percent of patients, the contact dermatitis is allergic in nature and may require referral to Dermatology or Allergy for formal patch testing and subsequent education targeted at allergen avoidance and alternatives. In the absence of formal patch testing, products can be recommended that contain low numbers of potential allergens to see if the dermatitis can be alleviated in this way and thus avoid the need for patch testing in some individuals.

Biography

Nicole M. Burkemper, MD, is an Associate Professor of Dermatology and Pathology at the Saint Louis University School of Medicine.

Contact: nburkem2@slu.edu