Aluminum has been reported to cause granulomatous dermatitis in the axillae. This reaction typically presents as red-brown, pruritic papules limited to the area in which deodorant was applied, with histopathology revealing epithelioid granulomas.49-51
Alum deodorants—considered a natural alternative—contain aluminum bound to potassium or ammonium in the form of a crystal or powder. Alum crystal deodorants have been reported to cause both a typical erythematous pruritic dermatitis as well as a granulomatous dermatitis with red-brown papules.52,53 The granulomatous dermatitis caused by either form of aluminum resolves with avoidance and use of topical steroids or topical tacrolimus.49,50,52,53
The diagnosis of aluminum ACD via patch testing may be identified with empty Finn Chambers, which are metallic aluminum, or with patch placement of aluminum chloride hexahydrate, though the former is only positive in patients with a strong allergy.54,55 In 2022, aluminum was named Allergen of the Year by the American Contact Dermatitis Society, with recommendations to conduct patch testing with aluminum chloride hexahydrate 10% rather than the traditional 2% to increase diagnostic yield.55 Additionally, it is recommended that aluminum be included in baseline patch testing for children due to the high prevalence of aluminum allergy in children and early exposure via childhood vaccines.54-56 In patients with aluminum allergy, providers may suggest purchasing aluminum-free deodorants or provide recipes for homemade deodorant that includes ingredients such as arrowroot powder, cornstarch, and diatomaceous earth.46
Nickel—Nickel is the most commonly identified contact allergen on patch testing yet an infrequent cause of axillary dermatitis. A case report from 2014 described axillary dermatitis in a woman that worsened during a positive patch test to nickel. Improvement was noted when the patient switched to titanium shaving razors.57 Nickel allergy also may present in the form of SCD. In one report, a woman developed dermatitis of the flexural areas, including the axillae, 3 months after undergoing a sterilization procedure in which nickel-containing tubal implants were placed.58 Patch testing revealed a positive reaction to nickel. The patient experienced complete resolution of the steroid-resistant dermatitis following removal of the implants via salpingectomy.58
FIGURE 2. Textile allergic contact dermatitis secondary to a deeply dyed blue sweater in a patient with positive patch test results to disperse blue 106, disperse blue 124, textile dye mix, formaldehyde, and methyldibromo glutaronitrile, among other allergens. The dermatitis involved the bilateral axillary rim and spared the vault.
Textile Dye—In contrast to dermatitis caused by deodorants/antiperspirants, contact allergy to textile dyes presents as dermatitis involving the axillary borders but sparing the axillary vaults (Figures 2 and 3).10 Other potential presentations of textile dye dermatitis include erythema multiforme–like eruptions and erythematous wheal–type reactions.59 Textile dyes are classified as disperse vs nondisperse, with the majority of contact dermatoses caused by disperse dyes, specifically Disperse Orange 1, blue 106, and blue 124.60-62 Ryberg et al61 found that the axilla is one of the more common locations to be affected by textile dye allergy, particularly in women, which was further supported by Seidenari et al,63 who found that skin folds were affected in 27% of study participants allergic to textile dyes (N=437), a finding that is likely due to friction, sweat, and occlusion.62 In one case report of a patient with dermatitis caused by reactive dyes, the garment required 3 washes before the patient experienced resolution of dermatitis.64 For patients with textile dye dermatitis, mitigation strategies include washing clothing before wearing, especially for darkly dyed items; avoiding tight clothing; wearing garments made of cotton, wool, silk, or linen; and choosing light-colored garments.9,64,65
FIGURE 3. Allergic contact dermatitis of the axilla suspected to be secondary to black textile dyes. The dermatitis resolved completely with avoidance of tightly fitted black clothing.
Axillary Dermatitis as a Manifestation of SCD and SDRIFE
Systemic contact dermatitis occurs when an individual who was previously sensitized to a particular allergen develops ACD of the skin with systemic exposure to that allergen or immunochemically related allergens. Exposure may occur via ingestion, inhalation, intravenous, intramuscular, and transepidermal routes.66 Systemic contact dermatitis manifests in a variety of ways, including focal flares at sites of prior contact dermatitis (recall reaction), vesicular hand dermatitis, intertriginous eruptions including axillary dermatitis, and generalized eruptions.67
Systemic contact dermatitis rarely involves systemic symptoms, and onset typically is within days of exposure. The 3 most common groups of allergens causing SCD are metals, medications, and plants and herbals.68 These allergens have all been reported to cause axillary dermatitis via SCD.58,69,70 Foods containing balsam of Peru that may lead to SCD include citrus, chocolate, tomato, and certain alcohols.70,71 Patients with a positive patch test to balsam of Peru may experience improvement of their dermatitis after reduction of balsam of Peru–rich foods from their diet.70 Metals implicated in SCD include mercury, nickel, and gold.72-74 Finally, PG ingestion also has been implicated in cases of SCD.37