Since the COVID-19 outbreak, countless studies have been conducted about the pandemic regarding people's physical and mental health, but there is a significant gap on the persistent effects on consumer behaviour. Hence, this thesis aimed to investigate if there is a relationship between the social constraints as a consequence of the COVID-19 pandemic and the potential increased engagement of post-purchase behaviour. The research focused exclusively on Swedish female millennials who are active social media users.    The research used a deductive approach by formulating hypotheses based on already existing theories. The explanatory design was used when aiming to investigate a causal relationship between two variables, i.e., prior to the pandemic compared to today. Further, a quantitative strategy was used by collecting primary data through a questionnaire, which thereafter was analysed through SPSS, using the paired sample t-test. To target the desired sample a convenience sampling method was used which collected a total of 226 respondents, with 197 valid participants. The sample was collected through several Facebook groups, combined with the utilizing of the authors own social media channels. Since this study aimed to measure engagement, the key concepts were converted in the survey questions to more specific terms, by a modified existing scale. Indicators were established to be able to measure the engagement under controlled conditions.   Furthermore, the results from the statistical tests resulted in a p-value to confirm or reject the null hypothesis, followed by a correlation coefficient value to determine the strength of the relationship. The empirical findings combined indicated significant evidence that because of the social constraints since the COVID-19 outbreak, there has been an increased engagement in the post-purchase behaviour on social media for Swedish female millennials. This was confirmed through a p-value of 0.000 in the t-tests for all seven hypotheses. Furthermore, all tests show correlation values between 0.449 and 0.617, which means that all the existing relationships are positive.    This means that during the period when COVID-19 has been an active societal problem with all its effects, the new living conditions have entailed an increased involvement in post-purchase behaviour on social media for Swedish female millennials. If corporations take these changed behaviours in consideration and adapt the marketing strategy accordingly, it  can contribute to increased sales as the credibility of the brand gets strengthened through the transparency that the customer base values.