A case report of allergic contact dermatitis to benzisothiazolinone in a laundry detergent

Benzoisothiazolinone (BIT) is one of the isothiazolinone derivatives which is widely used in household detergents, industrial products, cosmetic products, paints, adhesives, papers and in textile industry. Other isothiazolinone derivatives include methylchloroisothiazolinone (MCI), methylisothiazolinone (MI) and octylisothiazolinone (OIT), which may be present in laundry detergents.1 BIT and OIT are not permitted in EU cosmetic products. Cases of allergic contact dermatitis to laundry detergent have been reported in a 7-year-old girl who tested positive for MCI/MI with truncal dermatitis from clothing and a non-atopic factory worker involved in detergent production who tested positive for MCI/MI and MI with hand and pretibial dermatitis.2 We report a case of a 74-year-old non-atopic man who was referred to the dermatology department with a pruritic eruption affecting the legs, back, chest and inner thighs, sparing the genital area, for the last 8 years. There was an initial suggestion of a drug eruption due to rivaroxaban or bisoprolol, which had been started 3 weeks prior to the onset of the rash. The rash persisted despite changes in his medication. He had also changed his sofa twice, which made no difference. He plays guitar in a band. Multiple skin biopsies had been taken over the years, which had shown spongiotic and non-specific inflammation. On examination, there were ill-defined erythematous scaly patches on the torso and limbs, sparing the face, hands and feet. He was treated with various potency topical corticosteroids with minimal improvement. He could not tolerate azathioprine and declined further immunosuppressants. He was patch tested to the British Society for Cutaneous Allergy baseline series, cosmetic and fragrance series under occlusion with IQ Ultra chambers (Chemotechnique Diagnostics, Vellinge, Sweden) for 48 h. Patch test readings were conducted on Day 2 and Day 4, respectively, where he was positive for nickel + on Day 2 and ++ on Day 4. BIT was ++ on Day 4 only. Patient information leaflets for the relevant allergens were given to the patient. He returned 2 months later with complete clearance of his rash. He had found BIT in his Aldi laundry detergent. His skin had vastly improved with the switch to a different laundry product. There have been limited published reports of laundry detergents causing allergic contact dermatitis since the early 1970s when there were multiple reports highlighting optical brighteners and enzymes in laundry detergents causing allergic contact dermatitis.3 Ten common allergens in textile manufacturing and laundering products were reported to be benzisothiazolinone, benzyl benzoate, cocamidopropyl betaine, decyl glucoside, fragrances, lauryl glucoside, MI, MCI, phenoxyethanol and propylene glycol.4 Allergic contact dermatitis due to MI in laundry detergent has been previously reported,5 but in our case, testing to MI, 0.2% aq and MCI and MI 0.02% aq were negative. Although patient suspicion of their laundry detergent as a cause of dermatitis is high, a clear causal relationship between a detergent and the occurrence of dermatitis is often difficult to establish. BIT is a borderline irritant patch test material, and hence, uncertain patch test reactions are frequent. However, in this case there was rapid and complete clearance of long-standing intractable dermatitis on avoidance of BIT in laundry detergents. In the case of a clear-cut positive patch test reaction to BIT with no other identified source, patients should be advised to obtain information on the ingredients of their laundry detergent. From our patient's experience, benzisothiazolinone free laundry detergents are quite challenging to find. A study was done to analyse the concentrations of isothiazolinones in clothes after machine washing. The results revealed negligible isothiazolinone concentrations independent of the type of machine wash or material but showed the highest concentration of isothiazolinones in the control hand washing group.6 To our best knowledge, this is the first-ever reported case of allergic contact dermatitis to BIT containing laundry liquid with complete clearance of his dermatitis by the avoidance of such product. Mun Wai Lam: Writing – original draft; resources. Tang Ngee Shim: Writing – review and editing; supervision. The authors declare no conflict of interest.