Introduction: Recently in most countries there has been a continuous increase in the number of various allergic diseases. Early introduction of unmodified cow's milk (UCM) into the baby's diet may provoke the development of food allergies, allergic and food hypersensitivity reactions. Aim: The aim of our study was to examine the peculiarities of baby's nutrition in Ukraine, to estimate the impact of early cow's milk proteins (CMP) consumption on frequency of food hypersensitivity and allergic reactions in toddlers within two years of life, depending on the time of CMP introduction. Materials and methods: 5354 full term infants aged of 1–12 months were enrolled into the crosssectional study. Retrospective evaluation of incidences of food hypersensitivity and allergic reactions was done in a selected cohort of 1000 babies who were divided into 3 groups depending on their nutrition. 135 babies did not receive UCM (the first group). 471 – received UCM during the first year of life (the second group). 394 babies were fed with UCM starting from the second year of life (the third group). Results: Significant difference on frequency of food hypersensitivity reactions we found in 1, 2, 3 groups of toddlers when they consumed products that contained cow's milk protein (2.99% vs. 7.64% and 10.94%; p=0.01); eggs (2.22% vs. 8.49% and 10.41%; p=0.013); citrus (6.67% vs. 19.96% and 18.78%; p=0.001); chocolate (2.96% vs. 13.61% and 14.5%; p=0.002) and some other foods (4.44% vs. 14.01% and 10.41%; p=0.006). Conclusions: Introduction of UCM into baby's diet during the first and second year of life is associated with increased risk of a variety of allergic and food hypersensitivity reactions, accompanied by a higher frequency of hospitalizations and taking medications.