Introduction Henna tattoo application is a common practice in Eastern cultures but has become increasingly popular in the US as a form of temporary body art. The henna dyeing agent itself rarely leads to skin sensitization. The majority of cases of allergic contact dermatitis are associated with coloring agents, usually p-phenylenediamine (PPD). PPD is added to henna dye to make it darker and speed up the dyeing process. Case Description A 31-year-old healthy, Indian female who was also a first-year Allergy fellow, presented with intense itching and burning three days after the application (Panel B) of a temporary henna tattoo for her wedding (Panel A, original application). She began to have blistering on the fourth day (Panel C). After treatment with oral steroids, the dermatitis resolved without post-inflammatory hyperpigmentation. She previously had henna tattoos without reaction. T.R.U.E. TEST patch testing to 35 allergens (including PPD) and a negative control was negative. Additionally, patch testing to natural henna was negative also. Discussion In most cases, henna reactions are caused by chemical coloring additives, most commonly, PPD. Substances such as lemon, oil, vinegar, eucalyptus oil, and essential oils can also added to obtain different shades. Our patient's henna artist added a lemongrass-scented essential oil to the henna mixture. The essential oil used (unable to obtain for testing) may have been the sensitizing allergen. Allergists should be aware that the most common allergen may not be the culprit agent and more extensive testing may be required.