Dimethyl fumarate (DMF) has shot into prominence as an unexpected but powerful sensitizing agent. In fact, the American Contact Dermatitis Society conferred the dubious distinction of ‘Contact Allergen of the Year-2011’ on DMF.
DMF is a fine white crystalline powder, which is used extensively in the Asian leather furniture industry to prevent mold growth in finished leather products, including couches, recliners, sofas, and shoes.
The antifungal chemical is packaged in sachets, resembling the silica gel sachets put into electronic items and other moisture-sensitive products, including leather. However, silica gel does not adequately prevent fungal growth in larger leather items, especially during transport between varying climatic zones with different humidity levels. The moisture build up inside the closed container can be significant in humid locations. For this reason, DMF is used instead to protect such pieces. It evaporates and, thereby, prevents mold proliferation.
The DMF sachets are packed into the furniture in several ways. They may be fastened to the frame of the piece, or tucked under the leather upholstery. For smaller items, such as leather shoes, the sachets are put into the packaging.
DMF evaporates over time, and the vapor condenses and settles on the leather covering. It is this which is responsible for the allergic symptoms in hypersensitive individuals. These are typical of classic allergic contact dermatitis. The skin becomes red and swollen, with itching and scaling. The rash is papulovesicular and confined to the sites of exposure where the patient’s skin comes in contact with the seat or couch i.e., the back of the legs and buttocks, and the back. If the patient was reclining, the back of the arms may also be affected. This type of localization has led to its being called ‘sofa dermatitis’. The rash may be triggered by concentrations as low as below 1 ppm.
The chemical permeates fabric and clothing, which is why skin covered by clothes is also affected. The longer the person is exposed to it, and the more repeated such exposure is, the worse will be the symptoms. Thus severe cases may present as impetigo, a bacterial folliculitis, or mycosis fungoides. In such patients, hospitalization is required.
DMF can also cause eczema of the foot following exposure to DMF in shoes. If high concentrations are present, irritant contact dermatitis may occur instead. This may take the form of a rash with sharp edges, and which arises acutely following the use of a new pair of shoes, and which is limited to the area of contact with the shoe leather.
Other items which have been associated with DMF allergy or contact irritation include helmets.
The classic patch test is used to diagnose DMF allergy, using concentrations of 0.001 to 0.1% dimethyl fumarate in petrolatum or aqueous solution. Some researchers use an upper limit of 0.003-0.005% to prevent irritation.