Approximately 20% of the general population has a contact allergy.1 Allergic contact dermatitis (ACD) is a delayed type IV hypersensitivity reaction mediated by T lymphocytes.2 Axillary ACD presentation is variable but typically includes an eczematous eruption with erythematous scaly patches or plaques. Common products in contact with the axillae include deodorants, antiperspirants, razors, bodywash, and clothing.
Axillary skin is distinct from skin elsewhere on the body due to both anatomical characteristics and unique human self-care practices. Axillary skin has reduced barrier function, faster stratum corneum turnover, and altered lipid levels.3-5 Moreover, the axillae often are subject to shaving or other hair removal practices that alter the local environment, as layers of stratum corneum and hair are mechanically removed, which causes irritation and predisposes the skin to enhanced sensitivity to topical exposures.6,7 With the abundance of apocrine and eccrine glands, the axillae are prone to sweat, which also can accentuate contact allergy.2,3 Other factors, such as occlusion and friction, contribute to axillary contact allergy.8,9
Patch testing is the gold standard for the diagnosis of ACD and aids in identification of culprit allergens. A thorough patient history and examination of the rash distribution may provide further clues; for example, dermatitis due to a deodorant typically affects the vault, whereas textile dye dermatitis tends to spare the vault.10,11 Baseline-limited patch testing detects up to two-thirds of clinically relevant allergens.12 Therefore, patients may require subsequent testing with supplemental allergens.
The differential diagnosis for axillary lesions is broad—including inflammatory diseases such as irritant contact dermatitis and hidradenitis suppurativa, genetic disorders such as Hailey-Hailey disease, and infectious causes such as erythrasma—but may be narrowed with a thorough physical examination and patient history, histopathology, bedside diagnostic techniques (eg, scrapings and Wood lamp examination), and patch testing. Systemic contact dermatitis (SCD) or symmetrical drug-related intertriginous and flexural exanthema (SDRIFE) also may be suspected in cases of intertriginous dermatoses.
We review the potential allergens in products used on the axillae as well as the management of axillary ACD. We also discuss axillary dermatitis as a manifestation of SCD and SDRIFE.
Top Allergens in Products Used on the Axillae
Fragrance—A 1982 North American Contact Dermatitis Group study on cosmetic products identified fragrances as the most common cause of ACD,13 and this trend continues to hold true with more recent data.14 The incidence of fragrance allergy may be increasing, with positive patch tests to a fragrance chemical in 10% of patch test clinic populations.15 Fragrances are a ubiquitous ingredient in deodorants and antiperspirants, which are important sources implicated in the development and elicitation of fragrance ACD.16 One study found that fragrance was present in 97 of 107 (90%) deodorants available at Walgreens pharmacies.11
In a study of patients with a history of an axillary rash caused by a deodorant spray, Johansen et al17 reported that the likelihood of fragrance allergy is increased by a factor of 2.4. This risk of developing a fragrance allergy may be exacerbated in those who shave; Edman18 reported that the odds ratio of developing a fragrance allergy among men who shave their beards was 2.9. Although there are no specific data on the effects of shaving on ACD, shaving in general can induce localized irritation and increase percutaneous absorption.19