A 14-year-old girl developed 4 episodes of anaphylaxis of unknown etiology, which required intramuscular adrenaline administration each time. She had eaten pizza and a cheeseburger immediately before the first 2 episodes, respectively, but had not eaten anything for several hours before the last 2 episodes. It turned out that she had eaten the same ice lolly 4 hours before the first 3 episodes and a Café au lait Swirkle (a half-frozen beverage) 4 hours before the last episode. We detected carboxymethylcellulose sodium as the only common ingredient in all anaphylactic episodes. Skin prick tests were positive for carboxymethylcellulose solution and carboxymethylcellulose-containing food products. We obtained a custom-made carboxymethylcellulose sodium–free ice lolly from the manufacturer and confirmed that it did not induce anaphylactic reactions by a challenge test. Carboxymethylcellulose, an anionic water-soluble polymer derived from native cellulose, is considered to be unabsorbable from the human gut and has been widely and increasingly used in pharmaceutical preparations, cosmetics, and food. This article is the first report of anaphylaxis caused by carboxymethylcellulose-containing foods, whereas anaphylaxis to carboxymethylcellulose has been rarely associated with carboxymethylcellulose-containing pharmaceuticals. Although the exact mechanisms underlying the induction of late-onset anaphylaxis by carboxymethylcellulose remain unclear, a small minority of cellulose-digesting microbial flora in the human colon and contamination of food products with carboxymethylcellulose of low molecular weight might be involved. The induction of recurrent anaphylaxis by various products should be a clue that prompts physicians to suspect food additives as a cause for anaphylaxis.