Commentary

Over the past few years, there has been a major paradigm shift in the thinking about the prevention of allergic disease in children. Until recently, people thought that allergy could be prevented by preventing exposure to food allergens. Clinical trials appeared to support this by showing reduced prevalence of eczema in babies fed hydrolysed formula, as compared with cow's milk formula. Several international guidelines recommended hydrolysed formula for allergy prevention, and this became common practice throughout the western world.

A few years ago, we questioned the validity of this approach by highlighting methodological shortcomings in the allergy prevention literature.1 For example, the large differences in taste between cow's milk and hydrolysed formula preclude blinding of parents, which is important in studies with a subjective end point (eczema symptoms). In their clinical trial, Hill et al now reveal that inappropriate reporting of results of per-protocol analyses (instead of intention to treat analyses) may also have incorrectly made us believe that allergy prevention by dietary measures is useful. Their well-designed (and well-analysed) study clearly demonstrates that hydrolysed formula is no more effective than cow's milk formula in preventing allergic disease in ‘high risk’ children.

Their results make perfect sense in the light of certain other new findings. Recent observational studies have shown lower prevalence of cow's milk and peanut allergy in children exposed to the relevant allergen in early infancy than in children in whom exposure was delayed.2 Children without cow's milk allergy put on a milk-free diet may develop severe cow's milk allergy in the long run.3 Thus, in real life settings, ‘allergy prevention’ may be counterproductive by increasing the risk of food allergy. The current paradigm, therefore, is that early controlled exposure to food allergens is needed to develop and maintain tolerance to that food.

The time has come to admit the error of our ways, to stop medicalising healthy babies by providing them with hydrolysed formula, and to end the myth of allergy prevention by avoiding food allergens.