Cosmetic UV filter substances are known triggers for contact or photocontact allergies. UV filters contain reactive carbonyl groups, which are possible reaction partners for free amino acids or proteins from human skin, through which they can act as haptens. Prior screening using high performance thin layer chromatography (HPTLC) amino phase showed that commonly used UV filters with responsive ester groups were able to bind covalently to the amino side chains of the plate after heating and/or UV irradiation. The aim of the study presented here was to investigate the underlying reaction mechanisms and to assign possible reaction products for the UV   filter substances octocrylene (OCR), ethylhexyl methoxycinnamate (EHMC), ethylhexyl salicylate (EHS), octyldimethyl-p-aminobenzoic acid (OD‑PABA), and ethylhexyl triazone (EHT), using two primary amines, namely ethanolamine and butylamine, as reaction partners. Heating of the reaction batches completely transformed OCR into its corresponding benzophenone imines, while for EHS, EHT, and EHMC, ester aminolysis mainly yielded their respective amides. In the case of EHMC, a Michael-type addition reaction also occurred, which resulted in addition of the primary amines to the conjugated double bond. Further UV irradiation of the reaction batches slightly affected the product distribution of OCR and of EHMC, but not of EHS and EHT. The observed reactions generally had great influences on the absorption spectra. For EHS, a significant bathochromic shift and an increased absorbance were observed, while for EHMC, and especially for OCR, UVA+B efficiency was clearly lost. In contrast, for OD‑PABA, no reaction products could be generated under the conditions used.