Axillary granular parakeratosis. 
A 54-year-old woman had a 3 year history of a recurrent bilateral axillary rash during the summer months.  Both axillae showed hyperkeratotic, fissured and cobblestone plaques.  Skin biopsy showed the histology previously defined as axillary granular parakeratosis.  This finding may indeed represent an unusual contact reaction to anti-perspirants interfering with epidermal keratinization.