If you are writing an essay or a report and you want to avoid repetition, it can be useful to have some synonyms for the phrase "was allergic to". You may use "had an allergic reaction to", "was hypersensitive to", "had sensitivity to", "developed an allergy to", "experienced an allergic response to", "had a violent reaction to", "manifested an allergic sensitivity to" or "displayed an extreme reaction to". Using these synonyms can help you to vary your language and to improve the quality of your writing. However, it's important to ensure that you use synonyms correctly and that they don't change the meaning of your sentences.