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.