Allergic axillary dermatitis due to hydrogenated castor oil in a deodorant.

We present a case of axillary dermatitis caused by hydrogenated castor oil (HCO) in a commercially available deodorant. Patch testing with constituents obtained from the manufacturer showed allergic reaction to HCO 'as is', whereas there was no reaction to HCO 30% in pet. Testing 10 controls with HCO 'as is' did not cause irritant contact dermatitis. Allergic contact dermatitis to non-HCO in cosmetics has been described previously but sensitization to HCO seems to be rare. Most common allergens identified in deodorants are fragrances, and this case illustrates that HCO is another possible allergen found in this group of personal care products. It is important that it is tested 'as is' to avoid false-negative results.