Allergic Reaction is an episode of the ALVINNN!!! and The Chipmunks series.
While training for a TV baking competition with Eleanor, Theodore develops an allergy to an unknown ingredient.
Eleanor shows Theodore a clip of Meredith, their scary rival for a baking competition. In order to have a shot of beating her, the two practice their speed and teamwork. As they work on the frosting, Theodore accidentally throws the icing sugar the wrong way, covering Brittany and her flowers. The pair enjoy their cake as Alvin and Simon are drawn over by its sweet aroma. Theodore offers them some, though he suddenly starts sweating as he develops a rash and overheats before passing out. He wakes in the hospital and a doctor informs him he could be allergic to something in the cake so he must limit his diet to things that do not have sugar, flour, or eggs. Back at the Seville house, Theodore wakes in the night with a rumbling belly and sets out to find food. Dave hears him and Theodore uses the excuse of "homework" for being caught looking for "moldy sweets." When Dave tells Theo he threw everything away, Theodore throws a fit and storms off. When he gets to his room, he uses the zipline to loot the girls' treehouse for sweets, waking with a rash. Brittany, Eleanor, and Alvin do their best to prevent Theodore from eating sweets though he still manages to lick the batter spoon resulting in another reaction. That afternoon, the girls show Theodore a videotape of him stealing and he promises to not do it again, before he practices more with Eleanor. He frosts a cake, and when Eleanor doesn't believe he didn't eat anything as she took a call, despite him having another reaction, he decides to drop out of the competition. By evening at dinner, the Sevilles discuss with Theodore about the difficulty of dealing with his allergy, though Theodore is so upset about his limited diet that he launches into a temper tantrum. One night he had to have a revolting flavor of soup which Alvin, Simon and Dave tried, causing them to gross out. The following morning, Theodore sees Eleanor on the news and decides to help her, but he has another reaction during the competition. Waking in the hospital once again, they learn Brittany's flowers are to blame and now he can eat what he wants again.
- "Never Givin' It Up" 
- Goof: Eleanor and Brittany try to stop Theodore from eating the cake batter, but the bowl is missing when Eleanor and Theodore fall to the floor.
- This episode is the lowest viewed episode of the series to date.