Numerous types of thoughts pass through your mind over the course of a day. You may be reminiscing about your last vacation, thinking about a news story, recalling a funny conversation or brainstorming ideas for weekend plans. Not only are these thoughts highly prevalent in everyday life, but they also have wide-ranging impacts on how we function. Our research shows that different types of thoughts are meaningfully tied to emotional well-being. By understanding these connections, individuals can identify new ways to support and improve their mental health. This is especially pressing given the global increase in mental-health challenges, compounded by the shortage and burnout of mental-health professionals. Given these challenges, we believe expanding mental-health approaches to include prevention, in addition to intervention, may be important.Prevention initiatives will require an understanding of how clinically significant thought patterns arise in order to inform effective prevention strategies, which may ultimately prevent everyday stress from turning into mental-health problems.As a team of cognitive scientists who study mind-wandering and its ties to emotional well-being — as well as the brain and eye-movement patterns that support the wandering mind — we carried out several studies to examine the relationship between thoughts and emotions. In short, we found that what people think about is strongly linked to how they feel.Thoughts and feelingsIn a series of studies, we first set out to understand this relationship in the student population in Canada and the United States. Over the course of a week, we sent several short surveys to individuals every day asking them to report what type of thoughts they think about and how they feel. This allows us to capture their naturalistic thoughts and emotions in the moment as they go about their everyday life. We found that individuals tend to report worse mood when they experience off-task thoughts, often referred to as mind-wandering (for example, you may be thinking about what to make for dinner tonight while you are at work). In contrast, they tend to report better mood when they feel in control of their thoughts and can choose what to focus on (for example, your thoughts were focused on your partner during an important conversation with them). Individuals also report better mood when their thoughts flow freely from one topic to another. For example, your thoughts may go from childhood memories to a funny video to an upcoming vacation. The types of thoughts people experience are strongly tied to mood in the moment.Although these studies were helpful places to start, we were also curious about what the broader body of research found, especially whether the content of people’s thoughts matter for their mood. We identified 76 studies that examined a similar relationship, and performed a systematic review and meta-analysis to see what the overall evidence shows. Our review found that off-task thoughts are generally linked to feeling worse, especially when these thoughts feel out of an individual’s control, when they are ruminative and when they focus on negative topics. Importantly, thoughts can be linked to better mood, when they focus on the future or positive topics and when they flow freely from topic to topic. Put simply, what we think about can impact our happiness.Paying attention to thinking patternsHow can people leverage this knowledge to improve their mental health? An important initial step involves self-awareness, the process of paying attention to your thinking patterns and how it impacts how you feel. Although our findings suggest that certain types of thoughts are linked to mood variations in the general population, these relationships may be different for each individual. It is crucial to identify the thoughts that positively and negatively impact your own happiness. The next step is to explore strategies that can change the relationship you experience with your thoughts or directly change those thoughts. First, it’s important to normalize off-task thinking and even negative thoughts; they will arise for almost everyone in a given situation. They are not a “bug” in human thinking, but more likely a feature. Therefore, try adopting a mindful state of awareness, which involves not judging yourself and your thoughts, but instead acknowledging that negative thoughts come and go. Second, let’s consider ways to increase the types of thoughts that are linked to positive mood and decrease the types of thoughts that are linked to negative mood. For example, if you noticed that ruminative thoughts (for example, on a heated argument with a partner) put you in a negative mood, consider established strategies such as mindfulness, which has been shown to reduce ruminative thoughts. It’s worth noting that not every strategy works for every type of thought or for everyone; the key is to find what works best for you and the types of thoughts you want to change. Although we focused mainly on how thoughts can impact emotional well-being, it’s important to note that the opposite can also be true: how you feel may also impact what you think about. These strategies may help alter both thoughts and emotions.Noticing where thoughts go and learning how to change those thoughts as desired may help people feel happier and prevent everyday stress from developing into more serious mental-health challenges.Julia Kam receives funding from the Social Sciences and Humanities Research CouncilCaitlin Mills receives funding from the National Science Foundation and the Gates Foundation. She is affiliated with AugmentED, a program of AERDF.Jessica Andrews-Hanna receives funding from the National Institutes of Health.