Polypropylene based infant feeding bottles (baby bottles) are known to release microplastics which have the potential to cause health related issues. To the best of our knowledge, nanoplastic particles are thought to be even more hazardous for both our environment and the human health. Characterising particles on the sub-micrometre scale is challenging already for inorganic particles. In the case of nanoplastic particles additional challenges arise, making the use of conventional characterisation techniques virtually impossible. In cooperation with the start-up company “Brave Analytics”, opto-fluidic force induction characterisation was used to analyse nanoplastic particles generated during the use of baby bottles. Additionally, the influence of heat and general handling of the bottle on the amount of released particles is qualitatively described. For analysing microplastic particles we could draw on more established characterisation methods, like Raman spectroscopy. Baby bottles made from polypropylene were sterilised using 95 °C hot ultrapure water, subsequently filled with 70 °C hot ultrapure water and shaken. Afterwards the contents of the baby bottles were filtered. The loaded filters were then analysed using light microscopy and Raman spectroscopy. An average microplastic particle concentration of 3.2*107 particles per litre per baby bottle was determined. Electron microscopy images show alterations to the inner surface of the infant feeding bottle over the time of use. After sterilising the bottle, scales were found on the inner surface. These scales decreased in both size and number over the time of use. One can assume, that the thermal stress on the bottle during the sterilisation step is strong enough to damage the surface and particles make their way into the infant formula. Based on these findings, recommendations on the handling of baby bottles are developed to reduce the release of micro- and nanoplastic particles.