The individual fragrance components in deodorants most likely to cause ACD include hydroxycitronellal, eugenol, and geraniol—all constituent ingredients in patch test formulations of fragrance mixture I.11,20 Other common fragrance allergens associated with ACD include hydroxymethylpentylcyclohexenecarboxaldehyde, farnesol, and balsam of Peru.21-27 Hydroperoxides of limonene and linalool, common fragrances in detergents and personal care products, are increasingly recognized as contact allergens and have been reported to cause axillary ACD from deodorants.28-30
Dermatitis involving the bilateral axillary vaults wherever deodorant or antiperspirant was directly applied is the most common presentation of ACD due to fragrance (Figure 1).17 An eczematous eruption is common, though scale may be less apparent than in nonflexural regions. Axillary ACD secondary to fragrances also may result from use of fragranced laundry detergents, fabric softeners, soaps, and perfumes, and may spare the vaults.10,29,31,32 Less common presentations of axillary ACD due to fragrance include pigmented dermatoses; for example, ACD from an antiperspirant containing hydroperoxide of limonene presented as hyperpigmented patches with minimal erythema and scaling in the edges of the axillary folds.33,34
FIGURE 1. Allergic contact dermatitis of the axillary vault secondary to use of scented antiperspirant/deodorant in a patient with positive patch test results to propylene glycol, balsam of Peru, and quaternium-15.
Diagnosis of a fragrance ACD typically is made with a standard patch test series including fragrance mixture I and balsam of Peru, which may detect 75% and 50% of fragrance sensitivities, respectively.35 Patch testing may be followed with a repeated open application test of the product in question.36 Additionally, it may be appropriate to test for other fragrance allergens including balsam of Tolu, fragrance mixture II, lichen acid mix, and hydroxyperoxides of linalool and limonene (among other botanicals) if standard patch testing is negative and suspicion of fragrance ACD remains elevated.11
Propylene Glycol—Propylene glycol (PG)—a versatile substance that functions as a solvent, humectant, emulsifier, stabilizer, and antimicrobial—is the second most common contact allergen present in deodorants.11 It is prevalent in both personal care and household products, including deodorants, cosmetics, foods, toothpaste, cleaning agents, and detergents.11,37 Propylene glycol is both an allergen and an irritant. Among deodorants/antiperspirants, PG is both a common irritant and allergen, as its concentration may be particularly high (as much as 73%).38 One commonly reported example of PG contact dermatitis is from the topical medicament minoxidil.39,40
Patch testing data have demonstrated a positivity rate for PG ranging between 0.1% to 3.8%. The variability in these findings likely is due to differences in the tested concentrations of PG, as higher concentrations sometimes required to elicit an allergic reaction also may create a stronger irritation effect.41 Propylene glycol irritancy and the occlusive nature of the axillae may enhance sensitization to other allergens, as demonstrated by Agren-Jonsson and Magnusson,42 who reported sensitization to propantheline bromide and trichlorocarbanilide in patients who used a lotion with 90% PG. Many PG-containing products beyond deodorants/antiperspirants may be applied to the axillae, including steroid creams, lotions, shaving creams, and bodywashes.38,43
The diagnosis of PG allergy via patch testing is challenging and at times controversial given its irritant nature. False-positive irritant reactions have been documented, characterized by a weak reaction at 48 hours that is absent by 96 hours (decrescendo reaction). A reaction may not appear until 96 hours (crescendo reaction), which typically indicates a true contact allergy but in the case of PG also may be the substance acting as a “late irritant.”44 Fast (<24 hours) and well-demarcated reactions suggest irritation.45 Regardless, reactions to PG on patch testing, even those regarded as weak, may be considered relevant in consideration of the clinical context.37
Aluminum—Aluminum is the active ingredient in most antiperspirants, typically in the form of aluminum chloride, aluminum chlorohydrate, aluminum zirconium trichlorohydrex gly, or aluminum zirconium tetrachlorohydrex gly.46 Aluminum mechanically obstructs the eccrine glands to reduce sweat.47 Although aluminum is an uncommon allergen, a possible presentation of aluminum allergy is axillary vault dermatitis secondary to antiperspirant use.46 Another potential manifestation is a ringlike reaction to the Finn Chambers (SmartPractice) used in patch testing.46 In one case of aluminum-induced axillary dermatitis, a 28-year-old woman presented with eczema of the axillae, and subsequent patch testing revealed an allergy to aluminum chloride. The rash resolved upon cessation of use of an aluminum-containing deodorant.48