An allergic reaction is read as a strong rejection of something in your surroundings. Dream books see it as a sign that a person or a situation simply does not agree with you.
When this appeared in your dream, what were you feeling?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.