Under the acidic conditions of the stomach lumen, nitrosation reactions can occur in the human body between nitrite (added to meat because of its antibotulinic properties) and many compounds such as amino acids. From the results obtained, two conclusions can be drawn: (i) In the quantitative study of nitrosation reactions, it is necessary to take into account the competing reaction of HNO2 decomposition, which in some conditions is the dominant reaction; (ii) two alternative approaches based on the initial rate method are necessary to assess the weight of nitrous acid decomposition using taurine and homotaurine as nitrosatable substrates. In strongly acidic media, the decomposition reaction is dominant: In the case of taurine, the decomposition rate is negligible at pH ≥ 3.2. In the pH 3.2−2.5 range, decomposition is lower than nitrosation but not negligible, and at pH ≤ 2.5 decomposition is faster than nitrosation. With homotaurine, HNO2 decomposition is negligible at pH higher than 4.1. In the pH 4.1−2.8 range, nitrosation is faster but decomposition should be considered, and at pH ≤ 2.8 decomposition is the dominant reaction.