Does sensitization to foods in adults occur always in the gut?

It is widely accepted that, under normal conditions, the contact between allergens and the immune system via the gut results in immune tolerance. Thus, it is rather surprising that normal adults may become sensitized to foods that they have consumed a number of times without any consequence. However, the medical literature is crowded with reports suggesting that sensitization to food allergens may occur outside the intestinal tract in many instances. The present article reviews and discusses current data suggesting, either directly or indirectly, a possible initiation of food allergy in the respiratory tract or in the skin in the light of recent findings about mechanisms of tolerance and sensitization.