Is There Evidence That Alpha-Iso-Methylionone Causes Allergic Contact Dermatitis?

The fragrance material alpha-iso-methylionone, or ‘gamma-methylionone’, has been cited as a moderately frequent cause of allergic contact dermatitis. A review of the literature shows that when the underlying clinical and experimental data are analyzed, a clear cause-effect relationship has infrequently or rarely been established. On the basis of the generally weak sensitizing potential of this substance, coupled with its generally low exposure conditions, the prevalence of clinical cases would not be expected to be particularly high. This is not to say that alpha-iso-methylionone is a frequent inducer of low-intensity but sub-clinical, type IV allergy in members of the public. It remains to be seen however, how often such allergy, once established, is responsible for any of the cases of allergic contact dermatitis commonly ascribed in the literature. Indeed, in some cases, patch test conditions may not be optimal for differentiating between clinically relevant and irrelevant allergy to alpha-iso-methylionone. Prospective screening patch test studies combined with appropriate follow-up to ascertain clinical relevance should clarify these issues.