Compositae Allergy

Compositae allergy, also known as Asteraceae allergy, refers to allergic contact reactions caused by plants in the large Compositae family, which includes over 20,000 species of flowers, herbs, weeds, and vegetables such as daisies, sunflowers, and asters. The family name Asteraceae is derived from the Greek word "aster," meaning star, which reflects the star-shaped flower heads characteristic of these plants. These plants occur worldwide and are commonly found in gardens, roadsides, and natural landscapes.

The allergens most often responsible for reactions are sesquiterpene lactones, compounds present in the oleoresin fraction of the leaf, stem, flower, and sometimes even pollen. Because these allergens are widespread, exposure is common and reactions may arise from direct skin contact, airborne pollen, or even through cosmetic and skincare products containing Compositae extracts.

Compositae allergy usually manifests as contact dermatitis on sun-exposed skin. It is most common in middle-aged and older adults, particularly during summer months, though it can occur in individuals of any age and at any time of year. In certain regions, it is referred to as ragweed or parthenium dermatitis. Symptoms can also be triggered by ingestion of herbal supplements such as echinacea, leading to systemic reactions like angioedema, urticaria, or generalized dermatitis.

Clinically, the dermatitis can take several forms depending on the type of exposure. Hand dermatitis often develops in gardeners, farmers, or florists, with blisters, redness, or dry patches on the fingers, palms, or backs of the hands. Airborne contact dermatitis affects exposed areas such as the face, neck, and arms, producing redness, swelling, and blistering during pollen seasons. A seborrhoeic distribution may also occur, with lesions appearing in skin folds such as behind the ears, around the nose, or on the eyelids and neck. In severe cases, the reaction may spread to involve the entire skin surface, resulting in erythroderma. Chronic exposure can lead to photosensitivity, in which the skin reacts strongly to even brief sunlight exposure. Rarely, nodular prurigo-like lesions or stomatitis may occur if plant material is ingested.

Diagnosis is typically confirmed through patch testing. Standard baseline series include mixes of allergens such as sesquiterpene lactones or Compositae mixes, which contain compounds like alantolactone, costunolide, and dehydrocostus lactone. However, additional testing with individual plant extracts may be required, as patients often react to multiple related allergens. For example, reactions are frequently observed with parthenolide, dandelion, yarrow, feverfew, chamomile, arnica, and chrysanthemum extracts. Cross-sensitisation is common, meaning that individuals allergic to one plant extract often react to others with similar chemical structures.

Interestingly, more than one-third of patients with Compositae allergy also exhibit sensitivities to other plant-derived allergens, including fragrance mixes, balsam of Peru, and rosin. This overlap can make diagnosis and management more complex.

Compositae allergy typically persists for life, but symptoms can be controlled by identifying and avoiding the responsible allergens. This requires awareness of local plant species, careful inspection of cosmetic ingredient labels, and avoiding products that contain Asteraceae extracts. Most affected individuals can safely consume vegetables from the Compositae family, though highly sensitive patients may need to exercise caution.

Protective measures are crucial, especially during high pollen seasons. For individuals with occupational exposures, such as gardeners or florists, wearing protective clothing, gloves, and in some cases full coverage outdoors may be necessary to prevent airborne dermatitis.

Treatment depends on the severity of the dermatitis. Mild cases may improve with emollients and topical corticosteroids. More persistent or severe reactions may require oral antihistamines, systemic corticosteroids, or immunosuppressive agents such as azathioprine or ciclosporin. Patients with photosensitivity require additional sun protection to minimize flare-ups triggered by ultraviolet exposure.

Compositae allergy is an important but often under-recognized cause of contact dermatitis. While benign in most cases, it can have significant occupational and quality-of-life implications, particularly in individuals with chronic or severe reactions. Early recognition, appropriate patch testing, and long-term avoidance of triggers are key to effective management. Dermatologists play a critical role in guiding patients through diagnosis, education, and treatment, helping them maintain both skin health and overall quality of life.