Gluten in the classroom, measured

Play-Doh, paper mâché, pasta trays and cookie dough all contain wheat. A study from Children’s National Hospital measured how much of that gluten actually ends up on hands and tables — and the answer depended far more on the material than on the amount of gluten in it.

A gluten-free diet is usually discussed in terms of food: what is on the plate, what is on the label. But for a child with coeliac disease, a school day involves a lot of gluten that is never meant to be eaten — modelling dough, flour-and-water paste, pasta in a play tray, cookie dough in a cooking class. The question parents and teachers keep asking is how much of it ends up somewhere it could be swallowed.

Until 2020 there were essentially no measurements to answer that. A team at Children’s National Hospital in Washington, DC, with a co-author from Boston Children’s Hospital, set out to produce some, and published the results in the Journal of Pediatric Gastroenterology and Nutrition.

How the experiment worked

Thirty healthy children aged 2½ to 18, none of whom needed to avoid gluten — many were siblings of patients at the hospital’s coeliac programme — took part in simulated classroom activities. Each activity used ordinary gluten-containing materials: wheat-based Play-Doh, refrigerated cookie dough rolled out on a floured table, paper mâché made from wheat flour, salt and water, dry wheat spaghetti in a sensory table, and cooked, dyed spaghetti in the same kind of table.

To stand in for the food a child might eat next, the researchers rubbed a fresh slice of gluten-free bread over each child’s hands, and another over the table they had used. Each slice was homogenised and tested with the R5 sandwich ELISA, the method Codex Alimentarius endorses for measuring gluten in food. The assay detected down to 5 ppm and could quantify up to 84 ppm; anything above that was simply recorded as “>84”. After two of the activities, children were also randomly assigned to clean their hands with soap and water, water alone, or a wet wipe, and staff cleaned the tables the same way.

Dry was low, wet and sticky was high

The split the authors highlight is between dry and wet materials. Play-Doh itself was very high in gluten — a 3-ounce tub measured 32,253 ppm — yet after five minutes of play, every bread slice rubbed on children’s hands stayed under 20 ppm, and 27 of 30 had no detectable gluten at all. Dry spaghetti behaved the same way: nine of ten hand samples were below the 5 ppm detection limit.

The flour-based, wet activities were a different picture. After cookie-dough baking, paper mâché and play with cooked pasta, nearly every slice exceeded 20 ppm, and most exceeded the 84 ppm ceiling of the assay. Behaviour mattered too: the one cooked-pasta sample under 20 ppm came from a four-year-old who described the pasta as feeling like “gross worms” and visibly touched less of it.

What washing achieved

After Play-Doh, every one of the 60 hand and table samples taken after washing tested below 5 ppm, whichever of the three methods was used. After the baking project the result was more mixed. Hand cleaning worked well across all three methods, with one exception: a slice at 30.7 ppm from a four-year-old who had flour on their clothes, face and forearms as well as their hands. Tables were harder. Ten of the 30 cleaned work surfaces still transferred more than 20 ppm, and eight of those ten had been wiped with water alone, against one each for soap and water and for wet wipes. The authors conclude that soap and water was consistently the most effective method.

The study did not test washing after paper mâché or pasta play, and the authors list that as a gap.

Reading the numbers carefully

A parts-per-million figure here describes a slice of bread after it was deliberately rubbed across a child’s palms, fingers and the backs of their hands. It is a stress test of transfer, not a measurement of what any child actually swallowed, and the study did not try to estimate intake from habits such as thumb-sucking or nail-biting. The sample sizes were small — ten children for three of the activities — and the participants did not have coeliac disease, so no health outcome was measured.

The work was supported by philanthropic gifts from the Celiac Disease Foundation, Dr. Schär USA and Bia Diagnostics. The gluten-free bread used was a Schär product and Bia Diagnostics ran part of the testing, which the paper discloses. One author also disclosed advisory and research ties to pharmaceutical and diagnostics companies.

What the authors drew from it

Their conclusion is two-sided. Wet, flour-based activities carry a high risk of transfer, and for those the authors suggest gluten-free substitutes — paper mâché can be made with rice flour or cornstarch, and corn or rice pasta works in a sensory table. Low-transfer materials like Play-Doh and dry pasta, they write, may have been historically overestimated as a risk, provided the material itself is not eaten and hands and tables are cleaned afterwards. They also point to the social cost of excluding children from class activities, and call for further studies of cooking classes in particular.

For anyone new to these questions, celiac disease versus gluten sensitivity explains why trace amounts matter so much more in one condition than the other.

Source: Weisbrod VM, Silvester JA, Raber C, et al. A Quantitative Assessment of Gluten Cross-contact in the School Environment for Children With Celiac Disease. J Pediatr Gastroenterol Nutr, 2020;70(3):289–294.

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