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Background: Topical treatments of atopic dermatitis (AD) may be responsible for cutaneous allergies. Percutaneous sensitization to oat used in emollients/moisturizers has already been reported. Our objectives were to measure the prevalence of oat sensitization in AD children, to assess its relevance, and to look at related parameters.
Methods: We recruited prospectively children with AD referred for allergy testing between June 2001 and December 2004. Atopy patch tests (APT) and skin prick tests (SPT) to oat proteins (1%, 3% and 5%) and to the European standard series were performed followed by oral food challenge (OFC) and repeated open application test (ROAT) in the oat-sensitized group.
Results: About 302 children were enrolled. Oat APT and SPT were positive in 14.6% and 19.2% of cases, respectively. Children under 2 years of age were more likely to have positive APT. In oat-sensitized children, OFC and ROAT were positive in 15.6% (five of 32) and 28% (seven of 25) of cases, respectively. Thirty-two percentage of oat cream users had oat-positive atopy patch test (APT) vs 0% in the nonusers group.
Conclusions: Oat sensitization in AD children seen for allergy testing is higher than expected. It may be the result of repeated applications of cosmetics with oats on a predisposed impaired epidermal barrier. We suggest avoiding topical-containing oat proteins in infants with AD.
The prevalence of atopic dermatitis (AD) has not ceased to increase over the last 50 years in the countries of Northern Europe, from about 3% before the 1960s to 15–20% nowadays (1). Emollients/moisturizers are widely used as adjuvant therapies (2, 3). Several brands contain various molecules with a presumed or demonstrated anti-inflammatory role, such as oat proteins (4). A subgroup of patients with AD experiences a worsening of skin symptoms through contact with various allergens/irritants, including components of skin cosmetics. Contact allergy to oat protein found in moisturizers has been reported previously (5–10).
Our objectives were to measure the prevalence of sensitization to oat in children suffering from AD, to assess its relevance and to investigate associated or predisposing factors.
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- Patients and methods
In the population of children referred to our centre for allergy testing, nearly one-third was sensitized to oat. This finding is in itself surprising but may reflect the situation in France in children referred for allergy testing, as there was no major bias for severity of disease in this population of young children. The percentage of children having oat-positive APT decreased with age (Fig. 1). This significant correlation between age and oat APT results is in accordance with previous studies carried out with other allergens (23). It could be due to a more severe impairment of an immature epidermal barrier in young children (22). Indeed, the role of a genetically impaired epidermal barrier as the primary cause of AD and respiratory signs of atopy is now widely admitted and concerns several genes that encode for stratum granulosum/corneum proteins, i.e. filaggrin and LEKTI (24, 25).
Our study also showed that the prevalence of oat sensitization – measured with SPT or APT – was higher than in the four other published studies, whereas other tested allergens were in the same range of prevalence (Table 3). This may be due to the widespread use of oat-containing topicals from very early age in France, especially in AD-afflicted children. Indeed, 74.6% of children had previously been treated with emollients containing oat.
Concerning the oat APT results, no sensitization to oat could be detected in 65 AD patients in an Italian paediatric series (26). Moreover, APT was performed with a much lower oat concentration (0.007% and 0.7%) that was probably insufficient to detect oat-sensitized children.
Regarding the SPT results, the marked differences observed between our findings and those of the two studies published previously (27, 28) are difficult to interpret, as the allergen source was different as well as the SPT interpretation method. Moreover, one of the studies (28) concerned older AD patients (44 adults and six children), whereas ours was exclusively paediatric. This is in accordance with a recent study showing that oat-sensitized children may desensitize with age (29).
We found a poor correlation between positive oat APT/SPT and ROAT. First, this may be due to the fact that positive APT could be triggered with weaker concentrations than those used with ROAT because of occlusion (30). Secondly, as ROAT was performed at home by the parents, tests may have been carried out improperly. Thirdly, in children suspected of having oat allergy prior to the ROAT, including those who experienced skin manifestations when applying oat-containing creams and those with positive OFC, some of the parents may have refused the ROAT procedure, so the real percentage of children with positive ROAT may have been underestimated. While tests such as the ROAT increase the refinement of evidence-based diagnosis of clinical relevance (31), recent overviews have shown that it was negative in approximately half of the cases of seemingly reliable patch tests, that prolonged ROAT procedures (4 weeks or more) produce a higher degree of positivity, and that regional variation in reactivity may affect test results, with maximal reactivity in the upper back compared to the forearm (30, 31). Our ROAT-positive results are thus probably underestimated, so it is hardly surprising that at least one-third of our patients with positive APT and/or SPT have clinically relevant oat allergy.
A more frequent sensitization to oat pollen has been reported in farmers than in teachers, and cross-sensitization between wheat and oat has been shown in farmers (32, 33). In this study, we found no relationship between oat and wheat pollen environment and risks for oat sensitization. On the other hand, repeated application of cosmetics with oat components appeared to be an associated factor in our series. This is at variance with the work of Rancé and colleagues, in which oat APT were positive in four of 105 (3.8%) of the children using such creams and two of 98 (2%) of nonusers (27). However, in that study, the concentration of oat extracts was twofold less than in our study and children applying oat-based topicals used them for a shorter time. This argues in favour of percutaneous sensitization at a very young age.
While no oat-sensitized child experienced any severe reactions during OFC, five children did have positive reactions. The risk of percutaneous sensitization with food products is now considered real (34–37). For example, experimental studies in mice showed that ovalbumin exposure through the skin could trigger egg allergy, with a high level of ovalbumin-specific IgE and subsequent symptoms of systemic anaphylaxis during OFC (34). Moreover, T cells responsive to peanut antigens were found in the skin of an atopic infant before the development of peanut oral allergy (35). Furthermore, in a prospective study of 49 children with peanut allergy, a significant independent relation between peanut allergy and the use of cosmetics containing peanut oil was found (36). Thus, oat may be added to the list of food products (peanut, ovalbumin, almond, etc.) responsible for food allergy triggered by a possible percutaneous sensitization (37). In a very recent randomized-controlled study, it was shown that emollients containing oat proteins may reduce high-potency topical corticosteroid use in children with moderate-to-severe AD (38). That study argues in favour of the steroid-sparing effect of emollient therapy but the beneficial effect of oat proteins is unproven. As a safety-first principle to limit percutaneous sensitization by applying topical adjuvant treatments containing oat proteins, we recommend not using them before the age of 2 in predisposed children.