After more than a decade of use, topical minoxidil solution has proven to be a safe and effective treatment for androgenetic alopecia. However, some patients present with complaints of pruritus and scaling of the scalp. The most common causes of these symptoms include irritant contact dermatitis, allergic contact dermatitis, or an exacerbation of seborrheic dermatitis. Patients suffering from allergic contact dermatitis may benefit from patch testing to determine the causative allergen. Among the patients we patch tested, propylene glycol was found to be the contactant in a majority of cases, not the minoxidil itself. Many of these patients may be candidates for treatment with alternative formulations using other solvents, such as butylene glycol, polysorbate, or glycerol. Although predictive, patch testing results do not ensure that the compounded preparations will be tolerated. Unfortunately, patients found to be allergic to minoxidil are no longer candidates for topical treatment of their alopecia with any preparations of minoxidil.