Introduction: Organic biocides are often used for limiting the formation and spread of mould in living spaces. With these substances, we introduce a new possible risk to the health of people who work or live in such premises. Purpose: The aim of our study was to determine the physical and chemical factors that may influence the acceleration of octylisothiazolinone (OIT) excretion from interior wall paint coatings. We wanted to determine how extreme conditions, such as elevated relative humidity and elevated temperature, affect the release of OIT from the paint coating and to what extent the particle size of titanium dioxide (TiO2) affects its photocatalytic degradation. Methods: The main analytical method used was liquid chromatography in combination with a diode array detector. Paint coatings, prepared on tiles, were exposed in chambers that can provide extreme conditions as in living environments. Photocatalysis experiments were performed in a photoreactor with different TiO2 particle sizes. Results: The results obtained show that the OIT in the paint coating is affected by environmental influences such as elevated humidity and UV-A radiation, the same could not be confirmed for elevated temperature. The presence and particle size of TiO2 did significantly influenced decay of OIT. Discussion and conclusion: Our results and literature indicate that there is impact on organic biocides from the environment, such as relative humidity. The literature as our research indicate non-compatibility between the photoactive metallic oxides and the organic biocides, and that it is very difficult for user to predict the incompatibility between the colour and organic biocide. The developed methods and results of analyses allow further work, as they constitute the basis for a professional risk assessment in the case of the release of OIT from the paint coating.