T cell receptor sequence data of alopecia patients before and during sensitisation with diphenylcyclopropenone and healthy volunteers at equivalent timepoints, using the UCL Chain lab protocol. Details of the study are provided in Ronel et al, eLife 2021 (10.7554/eLife.54747). The processed data files have been generated using Decombinator V4 (https://github.com/innate2adaptive/Decombinator). The raw data files are available at the NCBI Sequence Read Archive, accession number PRJNA592875.