Killing mites with heat V. Mahakittikun*, S. Wongkamchai*, M. H. Ahamad, P. Vichyanond Key words: house-dust mite; heat; thermal death point. . HOUSE-dust mites may be effectively killed by high temperatures (1±3). We sought to investigate the effects of various forms of heat deliverance to household items at varying temperature upon the survival of house-dust mites. Cultures of Dermatophagoides pteronyssinus were used in four separate sets of experiments. In experiment 1, mites were plated in Petri dishes, and the effects of dry heat (incubator heat) and wet heat (hot water) at various temperature settings (40, 50, 60, and 708C) at 10, 20, 30, and 40 min were examined. In experiment 2, the effect of exposure to dry heat upon the behavior of mites placed in polyester membrane was examined. In experiment 3, we examined the effect of dry heat applied by ironing upon live mites placed on a cotton sheet and on a comforter of 2.5 cm in thickness. Temperatures at various ®ber layers of the comforter were measured. Mites were examined at various layers of comforter ®ber layer. Experiment 4 was set to examine the effect of sunlight and of vacuum-cleaning upon live mites seeded on to a straw mat. The survival of mites was determined by examining their shape and mobility. All experiments were performed in triplicates. The combination of a temperature of 508C or over with a duration of 20 min or more was suf®cient to cause 100% death of mites by dry heat. For wet heat, a temperature of 608C or over for 20 min or more was required to kill all mites. Mites were found to migrate into deeper layers of polyester ®ber in response to dry heat. Dry heat applied via ironing (408C for 5 s) killed all mites on a cotton sheet and on the top two ®ber layers of a comforter. Mites could survive this process in deeper layers of the comforter (40% and 93% in the third and fourth ®ber layers). Direct sunlight for 6 h, vigorous shaking, and vacuum-cleaning of the straw mat were not effective to kill or remove mites from the mat since mites could hide in the cracks or cling very tightly to mat ®bers. In our experiments, dry heat seemed to be more effective than wet heat. With a hot wash of over 608C, a duration of more than 20 min is necessary to kill all mites. Ironing is effective for killing mites on thin sheets, but not on thick clothes or comforters. A straw mat supports the survival of mites well and should not be used by mite-sensitive individuals. *Department of Parasitology Faculty of Medicine of Siriraj Hospital Mahidol University Bangkok Thailand Accepted for publication 30 October 2000 Allergy 2001: 56:262 Copyright # Munksgaard 2001 ISSN 0105-4538 References 1. MCDONALD LG, TOVEY E. The role of water temperature and laundry procedures in reducing house dust mite populations and allergen content of bedding. J Allergy Clin Immunol 1992;90:599±608. 2. KINNAIRD CH. Thermal death point of Dermatophagoides pteronyssinus (Trouessart, 1897) (Astigmata, Pyroglyphidae), the house dust mite. Acarologia 1974;29:455±461. 3. TOVEY E, WOOLCOCK AJ. Direct exposure of carpets to sunlight can kill all mites. J Allergy Clin Immunol 1994;93:1072±1074. Dry heat or prolonged washing is needed. Exanthema to metamizole D. Quin Äones Este Âvez*, C. Ferna Ândez Schmitz Key words: biopsy; ®xed exanthema; metamizole; nonpigmented. . FIXED exanthema is a fairly common dermatologic condition with repeated episodes of cutaneous in¯ammation appearing characteristically at the same sites (1). The responsible agent is a drug in 85% of reported cases. That constitutes 10% of all adverse drug reactions. The drug most frequently involved is trimethoprim-sulfamethoxazole. Nonsteroi- dal anti-in¯ammatory agents are known to cause adverse drug reactions. Fixed exanthemas caused by metamizole have already been reported (2±4). There is a nonpigmented form of ®xed exanthema. It is a distinctive entity, as proposed by Abranowitz & Noun in 1933 (5). It has no residual pigmentation or any other trace. The epidermis is not disturbed, and thus no pigmentation occurs. In this case, the dermis is the primary site of the drug sensitivity response. Cases are reported to have been caused by sensitivity to ephedrine and pseudoephedrine (6±8). We report a case of nonpigmented ®xed exanthema caused by Nolotil 1 (metamizole). In our case, histologic features revealed new data. A 58-year-old woman with arterial hypertension controlled with a 5-mg dose of amlodipine (Astudal 1 ) once a day was referred to our clinic for a cutaneous disorder. In the last two years, she had showed oval, well-de®ned, nonitching erythematous lesions with slightly desquamative surface. These lesions First case of nonpigmented ®xed exanthema. 262