Axillary granular parakeratosis.

The term axillary granular parakeratosis is proposed for a unique axillary eruption with distinct histopathologic features. Four middle-aged to elderly patients (three women, one man) had unilateral or bilateral, usually pruritic, hyperpigmented to bright red patches in the axillae. Biopsy specimens revealed severe compact parakeratosis with the stratum corneum measuring 80 to 250 microns in maximal thickness, maintenance of the stratum granulosum, remarkable retention of keratohyaline granules throughout the stratum corneum, and vascular proliferation and ectasia. A contact reaction to an antiperspirant/deodorant is suspected as the cause. We speculate that the offending agent alters the maturation sequence of the stratum granulosum and stratum corneum, possibly by interfering with the degradation of filaggrin precursor to filaggrin units.