• Protein modification significantly decreased the allergenic reactivity of α-Lactalbumin. • The type, number and location of the modified sites affected allergenic reactivity. • Shielding effect and conformational changes reduced allergenic reactivity of α-Lactalbumin. Bovine α-lactalbumin (α-Lac) allergy is a common health problem. This study assesses the allergenic reactivity and the structural properties of α-Lac after protein modification (glycation, phosphorylation and acetylation) by ELISA, cells experiment and high-resolution mass spectrometry. Three modified methods significantly reduced the IgE/IgG-binding capacity, and the release of histamine and interleukin-6, and changed the conformational structure of α-Lac. α-Lac was glycated at K13, K16, K94, K98, and K108, phosphorylated at Y18, S22, Y103, and S112, and acetylated at K13, T33, S34, T38, S47, K62, S69, S70, K108, and K114, respectively, leading to masking the linear epitopes of α-Lac. Therefore, the decrease of allergenic reactivity of α-Lac induced by glycation, phosphorylation and acetylation depends upon not only the shielding effect of their modified sites, but also the change of conformational structure. This study confirmed that protein modification was a promising method for decreasing the allergenic reactivity of allergic proteins. [ABSTRACT FROM AUTHOR]