Labiatae allergy: systemic reactions due to ingestion of oregano and thyme

There are no cases described in the medical literature of systemic allergic reactions due to oregano (Origanum vulgare) or thyme (Thymus vulgaris). These herbs belong to the Lamiaceae (Labiatae) family which comprises other plants such as hyssop (Hyssopus officinalis), basil (Ocimum basilicum), marjoram (Origanum majorana), mint (Mentha piperita), sage (Salvia officinalis) and lavender (Lavandula officinalis).

We describe three systemic allergic reactions caused by oregano and thyme in the same patient.

Skin tests with inhalant allergens and plants of the Labiatae family were done. We used the prick by prick technique with dried commercial plants and prick tests with extracts prepared with the Frugoni method in our patient and in ten control patients. Total serum IgE was determined by Phadezym IgE PRIST (Pharmacia). Specific IgE was measured by two methods: CAP system (Pharmacia) and Phadezym RAST (Pharmacia Diagnostics, Uppsala, Sweden) with activated discs of the allergenic extracts that were prepared in our laboratory.

Skin tests with inhalants were positive to grasses. Skin tests with plants of the Labiatae family were positive in all cases when the skin prick technique was used; tests were negative with basil and lavender, and positive with all the others when we used the prick by prick technique. We did not detect any positive skin tests nor specific IgE to plants of the Labiatae family in control patients. Total serum IgE was 406 U/mL. Specific IgE was detected to all herbs tested; higher levels were obtained with the CAP system.

Plants belonging to the Labiatae family seem to show cross-sensitivity on the basis of clinical history and in vitro and in vivo test results.