Mental Health Conditions A mental illness is a condition that affects a person's thinking, feeling or mood. Such conditions may affect someone's ability to relate to others and function each day. Each person will have different experiences, even people with the same diagnosis. Recovery, including meaningful roles in social life, school and work, is possible, especially when you start treatment early and play a strong role in your own recovery process. A mental health condition isn’t the result of one event. Research suggests multiple overlapping causes. Genetics, environment and lifestyle influence whether someone develops a mental health condition. A stressful job or home life makes some people more susceptible, as do traumatic life events like being the victim of a crime. Biochemical processes and circuits and basic brain structure may play a role, too.