Wild silk allergy has been described in recent years as a cause of nightly asthma due to contact with bedcovers containing wild silk or silk waste (1). Possible allergens are either products or parts of the silkworm Antheraea pernyi, the producer of true wild, or tussah, silk, or of Bombyx mori, the producer of cultivated silk in the case of wrongly labeled products. Another possible allergen derives from an insect of the genus Anthrenus, which feeds on cocoons and other insects and has been found as a contaminant in silk waste-containing bedcovers (2).
In addition to bedcovers, silk is used in a variety of products, such as fillings in jackets or sleeping bags and clothing such as scarves and ties. Here we describe a patient who developed asthma while wearing a silk cardigan.
During a summer vacation in Ireland, a 27-year-old woman suffered from asthmatic symptoms during a train ride from Cork to Limerick. These symptoms occurred also upon her return to Switzerland. The patient noticed asthma during the daytime in increasing frequency, finally causing her to consult a general practitioner, who referred her to our department.
In her personal history, wild silk sensitization causing asthma during the night had been diagnosed years before. The patient had since then removed the bed quilt and all other wild silk-containing materials from her home.
Skin prick testing of a screening series revealed a positive reaction to wild silk (++++). Specific IgE (CAP-FEIA, Pharmacia Upjohn, Uppsala, Sweden) for wild silk was 17.7 kU/l; for silk, 3.7 kU/l. In addition, specific IgE for mugwort was 4.12 kU/l and for a screening test for domestic allergens Rx2 (cat and horse epithelia, dog dander, Dermatophagoides farinae, and Alternaria), 0.68 kU/l. Lung-function and bronchial provocation tests with methacholine were normal.
At first, pollen sensitization seemed to offer an explanation, as the symptoms had started during a train ride with open windows, but, as symptoms persisted during autumn and winter, this became improbable. On further questions about new items, the patient showed a new cardigan, seemingly made of wool or cotton, she had bought during her day trip to Cork. Inspection of the label revealed that the cardigan had been made in China and contained 20% cotton and 80% silk. Skin prick testing of some fibers of the cardigan eluted in water (Fig. 1) gave a strongly positive reaction (+++).
We diagnosed asthma induced by silk sensitization. As the cardigan had become one of the patient's favorite clothes, which she had been wearing more and more often, thus carrying the allergen with her, an increasing frequency of asthmatic symptoms had developed. When she stopped wearing the cardigan, the asthmatic symptoms disappeared completely.
Silk allergy in the silk industry affecting mainly spinners and weavers has been recognized for years, while allergic reactions of consumers on a large scale have been reported for the first time with occurrence of nightly asthma caused by silk waste-containing bed quilts.
Allergy to silk clothing is rare, since washing and heating of the silk in an alkaline environment for better separation of the silk thread formed by two fibroin filaments glued together by sericin, removes the sericin, which is the main allergen. Removal of the sericin often is done after spinning and weaving, as it offers a good protection against mechanical friction during processing.
Fibroin, the protein substance of silk, has a low allergenic potential. Scarves, ties, and other clothes made of washed silk are safe for the consumer, and only single cases of allergy to silk clothes were reported in the 1930s (3–5).
A series of children with asthma induced by silk waste-filled jackets has been observed in China (6). The cardigan of our patient contained no silk waste but seemingly was made of unwashed mulberry silk or wild silk, resulting in a “cotton or wool appearance”, while still containing the allergen.