Sensitization potential of hydrolysed wheat proteins.

In this issue, Nakamura et al. (1) report on the cross-reactivity between different types of hydrolysed wheat protein (HWP). As mentioned in their introduction, a few years ago >2000 Japanese citizens developed severe contact urticaria and immediate-type systemic reactions, which could be attributed to the use of a particular brand of facial soap. Eventually, an additive in this soap, HWP, was identified as the cause. Several authorities, including the European Commission, took note of this issue, resulting in an opinion on the safety of HWP by the SCCS [SCCS/1534/14 (2)]. Although the ‘epidemic’ may have been incidental and restricted to Japan, and is apparently under control, there are a few aspects that may be of interest to the readership of this journal. This editorial is based on the SCCS opinion, of which the author was the rapporteur; for a more extensive discussion of the topic, the reader is referred to that document. HWPs are manufactured from wheat, mostly by an enzymatic method, but other procedures, such as acid hydrolysis, are also used. The process generates protein fractions with a wide range of molecular weights. HWPs are widely used in products applied to the skin, such as soaps and shampoos, shower gels, bath oils, and facial care products. This is because of their surfactant, film-forming, foaming, hydrating and softening properties. The INCIname is ‘hydrolysedwheat protein’ (CASno. 94350-06-8/222400-28-4/70084-87-6), but other terminology is also used, including ‘hydrolysedwheat gluten (extract)’, ‘hydrolysed wheat germ extract’, and others (http://ec.europa.eu/growth/tools-databases/cosing/, last accessed 4 February 2016). HWPs can also be present in food, in particular ham and pâté. Therefore, human exposure is widespread. Being proteins, HWPs can generate immediate-type immune responses. Cases of contact urticaria and systemic reactions caused by cosmetics containing HWPs havebeen reported, but, besides the above-mentionedparticular episode in Japan, such reactions appear to be rare, or may have hitherto been overlooked. Most cases have been seen in France (3, 4). It is interesting to note that, although a few patients also reacted to food products that contained HWP, all of these patients could eat bread, baked products or pasta without problems. In contrast, a number of the Japanese patients also experienced systemic reactions after eating natural wheat proteins, such as bread. This points to differences in the immunoreactive profiles among the HWP-sensitized individuals. Clinical reactions from eating wheat-based food are not common, given the widespread consumption of bread, pasta, etc. It is of note that wheat allergy is not the same as coeliac disease; the latter is an abnormal cellular response to gluten. Allergologists are familiar with wheat-dependent exercise-induced anaphylaxis (WDEIA), which is associated with serum reactivity to ω-5 gliadin in wheat. In children with allergic reactions after eating wheat, ω-5 gliadin is the most prominent allergen. In bakers who have been sensitized to wheat by inhalation (bakers’ asthma), other wheat proteins (mainly α-amylase/trypsin inhibitors) are the main culprits, and most bakers with this condition can eat bread and pasta without problems. A number of the above-mentioned Japanese patients had also developed WDEIA, but their serum showed no reactivity to ω-5 gliadin. Therefore, a distinction between conventional WDEIA and HWP-WDEIA has been proposed. The Japanese experience supports the notion that skin exposure to proteins is an important route for the induction of (immediate-type) sensitization (5). It calls into question whether cosmetics should contain proteins that are present in an important commodity such as food. One solution to this problemmay be tominimize the size of the proteins that are put on the skin. For the cross-linking of IgE (which is essential for elicitation of an allergic reaction), the minimum molecular weight of an allergen is assumed to be in the order of 3000 (6), which may suggest that this would also be an appropriate threshold for the induction of IgE-mediated sensitization. BeyondHWP, for natural cosmetic oils in which protein is not an essential ingredient, such as cosmetic-grade peanut oil, minimizing the protein content should certainly be attempted [SCCS/1526/14 (7)].