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Author: Vanessa Ngan, Staff Writer, 2012.
Dimethyl fumarate (DMF) is a potent allergenic sensitiser that is used for its antifungal properties. It is good at stopping the growth of mould in finished products such as leather couches and shoes. The white crystalline powder is packaged into small sachets, similar to silica gel sachets used to remove moisture. Whilst silica gel is an inert substance that removes moisture, it is not that effective in preventing mould growth in large leather items, hence the use of DMF sachets.
DMF sachets are found stapled to the wooden frame or directly under the leather covering of couches. They are also placed directly into packaging such as shoe boxes. Although finished leather goods hold very little moisture and, therefore, not prone to mould, the problem arises when transporting these items between different climates. Confined spaces and humid environments can lead to moisture build-up and mould growth. The crystalline DMF powder works to prevent mould growth by evaporating over time. However, during this process it also permeates the leather goods.
In DMF allergic individuals, contact with DMF produces classic allergic contact dermatitis. In high enough concentrations it may also cause irritant contact dermatitis. The skin affected by the dermatitis can be severe, red, swollen, scaly and itchy. The rash is often seen on the backs of the legs, buttocks and back of patients who have sat on a DMF-contaminated couch. Hence the condition is commonly known as “sofa dermatitis”. Very low levels of DMF (<1ppm2) can trigger a reaction in individuals who are sensitive to the substance. DMF can permeate fabric so areas of skin covered in clothing may also be affected. Continued and repeated exposure to DMF will lead to worsening of symptoms.
Back in 2006-8 there was an outbreak of furniture-related dermatitis in Finland, UK and France. In some cases the rash was quite severe, resembling mycosis fungoides or septic infections (impetigo), and required hospitalisation. Thorough investigation led to the discovery that all patients had purchased leather furniture prior to developing the dermatitis and all the furniture was traced back to a furniture factory in China whom was using DMF to prevent mould growth.
DMF has also been implicated in foot / shoe dermatitis. In one case the dermatitis started as an acute, sharply demarcated eczema that matched exactly to the contact area of the shoe exposure. The patient had worn a pair of new shoes for approximately 8 hours. The high concentration of DMF produced an irritant contact dermatitis rather than allergic contact dermatitis.
Dimethyl fumarate was declared the Contact Allergen of the Year for 2011 by the American Contact Dermatitis Society (ACDS).
DMF allergy is diagnosed by performing special allergy tests, i.e. patch tests. Concentrations of 0.001 to 0.1% dimethyl fumarate in petrolatum or aqueous solution can be used for patch testing. However, due to the high risk of irritant reactions and active sensitization caused by DMF some researchers have recommended concentrations of 0.003% or 0.005% as an upper limit. Currently DMF is not included in most baseline series for patch testing and more studies are required to determine the exact concentration of DMF to be used.
Confirmation of DMF allergy requires the prompt removal of the causative agent and then management as for any acute dermatitis/eczema; this may include treatment with topical corticosteroids and emollients. In severe cases, patients may be hospitalized and treated with systemic steroids.
In the European Union, the use of DMF has been banned since 1998. In January 2009, the European regulators also banned the import of products containing DMF as a result of severe cases of dermatitis caused by DMF in imported products. However, in the United States and Australasia there is no regulation of products containing dimethyl fumarate.
Recently in Australia there have been reports of DMF sachets found in imported children's school shoes. Tests performed by the Council of Textile and Fashion Industries showed that 25% of shoes bought from major retailers contained DMF.
If you have sensitivity to DMF you should clearly avoid any contact with products that may have been contaminated with the substance. Sachets labelled “mould inhibitor” or “anti-mould” are likely to contain DMF and should not be touched. Sachets commonly found in shoe boxes or other packaged goods, labelled “silica gel”, should be handled with caution as it has been discovered that some of these may contain both silica gel and DMF, but are labelled only as silica gel sachets.
Items such as shoes that have been in a box with DMF sachets should be left for several months in the open air before the level of DMF can be considered harmless. Unfortunately, in some shoes DMF may have been incorporated into the structure of the shoe and the evaporation of DMF to reach safe levels may be years instead of months.
It is difficult to avoid DMF as products are not identified as containing the substance. Patients and doctors need to be aware of DMF allergy if unexplained skin reactions occur, particularly if a new item of furniture or clothing has been purchased recently that coincides with the dermatitis. Your dermatologist may have further specific advice, particularly if you are highly sensitive to DMF.
CAS number: 624-49-7
Appearance: fine white crystalline powder
Sensitizer: dimethyl fumarate
Patch test: 0.001 to 0.1% dimethyl fumarate in petrolatum or aqueous solution
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