Allergic Contact Dermatitis Caused by Isothiazolinones in an Ultrasound Gel: Need for Stricter Regulation of Topical Medical Devices

A 74-year-old non atopic retired male presented with weeping dermatitis that had been recurring for almost 2 years. His past medical history included vitiligo and osteoarthritis. The symptoms of his dermatitis had started a few weeks after repeated bi-weekly physiotherapy under ultrasound (US) guidance which included the topical application of LCH Supragel (Turkuaz, Istanbul, Turkey) always on the back, lower and upper extremities. After each application the gel was wiped off, without being completely cleaned and removed. He had already consulted several dermatologists and symptoms improved with topical corticosteroids yet reappeared upon discontinuation. Upon clinical examination, he had pruritic, erythematous oozing dermatitis affecting the lower back, buttocks, upper and lower limbs (Figure 1A,B).

The US gel was labelled as ‘no formaldehyde, paraben free, salt free, PVC free, water soluble’ without a list of ingredients. The safety data sheet (SDS) declared the contents as methylchloroisothiazolinone(MCI)/methylisothiazolinone(MI), carbomer, triethanolamine, monopropylene glycol.

Patch tests were performed with the European baseline, cosmetics and plastics/glues series (Chemotechnique Diagnostics, Vellinge, Sweden) using IQ-Ultra chambers (Chemotechnique Diagnostics) on Hypafix tape (BSN medical, Stockholm, Sweden). A semi-open test was performed with LCH Supragel ‘as is’. Readings per ESCD guidelines showed positive reactions on day(D) 2 and D3 to MCI/MI (+++) 0.02% aq. and to MI alone (+++) 0.2% aq. (with MCI/MI>MI) (Figure 1C), benzisiothiazolinone (+), dimethylaminopropylamine (++). No reaction was observed with triethanolamine and propylene glycol. Carbomer was not tested. The semi-open test with LCH Supragel was positive (+) on D3.

The dermatitis healed completely with topical corticosteroids and avoidance of the US gel.

Allergic contact dermatitis (ACD) due to isothiazolinones contained in an US gel has been described in both non-occupational [1] and occupational [2-4] settings (Table 1). Supragel was marketed as ‘hypoallergenic’ and the labelled constituents did not declare any isothiazolinones. However, its SDS disclosed the mixture of MCI and MI (< 0.0013%) in a 3:1 ratio.

European legislation prohibits the use of MCI/MI in ‘leave-on’ products, but permits the use of a mixture of MCI/MI at a maximum of 0.0015% (15 ppm) in a 3:1 ratio in ‘rinse-off’ cosmetic products. Currently, there is no equivalent legal requirement for non-cosmetic products, particularly not regarding ‘topical’ medical devices. Although the concentration of MCI/MI in Supragel is below the permissible limit of rinse-off products, it is only sparsely removed with a tissue paper without actually immediately and thoroughly cleansing the skin with water. Our patient developed ACD after a few applications of the US gel. Taking into account the frequent and repeated application on the same skin area, it might be hypothesised that the US gel behaves more like a leave-on product, hence, facilitating sensitization.

Our case reinforces the urgent need to modify the European legislations regarding topical medical devices, that is, harmonising them with the Cosmetics regulation, in order to enhance patient safety [5].

Goël Fenech: conceptualization, investigation, writing – original draft, writing – review and editing. Lynda Bensefa-Colas: writing – review and editing, supervision. Marie-Noëlle Crepy: conceptualization, writing – review and editing, supervision.

The patient in this manuscript has given written informed consent to publication of their case details and photographs.

The authors declare no conflicts of interest.