Calcareous soils of central and southwest China are home to Primula obconica1 (also known as German primrose and Libre Magenta).2 Primula obconica was introduced to Europe in the 1880s, where it became a popular ornamental and decorative household plant (Figure).3 It also is a frequent resident of greenhouses.
Primula obconica is a member of the family Primulaceae, which comprises semi-evergreen perennials. The genus name Primula is derived from Latin meaning “first”; obconica refers to the conelike shape of the plant’s vivid, cerise-red flowers.
Allergens From P obconica
The allergens primin (2-methoxy-6-pentyl-1,4-benzoquinone) and miconidin (2-methoxy-6-pentyl-1, 4-dihydroxybenzene) have been isolated from P obconica stems, leaves, and flowers. Allergies to P obconica are much more commonly detected in Europe than in the United States because the plant is part of standard allergen screening in dermatology clinics in Europe.4 In a British patch test study of 234 patients with hand dermatitis, 34 displayed immediate or delayed sensitization to P obconica allergens.5 However, in another study, researchers who surveyed the incidence of P obconica allergic contact dermatitis (CD) in the United Kingdom found a notable decline in the number of primin-positive patch tests from 1995 to 2000, which likely was attributable to a decrease in the number of plant retailers who stocked P obconica and the availability of primin-free varieties from 50% of suppliers.3 Furthermore, a study in the United States of 567 consecutive patch tests that included primin as part of standard screening found only 1 positive reaction, suggesting that routine patch testing for P obconica in the United States would have a low yield unless the patient has a relevant history.4
Clinical features of P obconica–induced dermatitis include fingertip dermatitis, as well as facial, hand, and forearm dermatitis.6 Patients typically present with lichenification and fissuring of the fingertips; fingertip vesicular dermatitis; or linear erythematous streaks, vesicles, and bullae on the forearms, hands, and face. Vesicles and bullae can be hemorrhagic in patients with pompholyxlike lesions.7
Some patients have been reported to present with facial angioedema; the clinical diagnosis of CD can be challenging when facial edema is more prominent than eczema.6 Furthermore, in a reported case of P obconica CD, the patient’s vesicular hand dermatitis became pustular and spread to the face.8
Patch testing is performed with synthetic primin to detect allergens of P obconica in patients who are sensitive to them, which can be useful because Primula dermatitis can have variable presentations and cases can be missed if patch testing is not performed.9 Diagnostic mimics—herpes simplex, pompholyx, seborrheic dermatitis, and scabies—should be considered before patch testing.7
Prevention and Treatment
Preventive Measures—Ideally, once CD occurs in response to P obconica, handling of and other exposure to the plant should be halted; thus, prevention becomes the mainstay of treatment. Alternatively, when exposure is a necessary occupational hazard, nitrile gloves should be worn; allergenicity can be decreased by overwatering or introducing more primin-free varieties.3,10