Results from recent epidemiological studies strongly suggest that ingestion of food promotes immune tolerance to food antigens, whereas exposure to food antigens through skin leads to allergic sensitization. A "dual-allergen-exposure hypothesis" has been proposed to explain those findings. However, several other recent studies have demonstrated that some allergic diseases can be successfully treated by recurrent epicutaneous exposure to allergens. At a glance, these two sets of findings seem to be contradictory, but we think they provide important clues for understanding the mechanisms behind the allergy march. Here, we propose that per-"eczema"tous sensitization drives the allergy march, and we introduce results from several published studies in support of this hypothesis. We hope that this review may help in establishment of new strategies for preventing the allergy march in the near future.