Either having a medical illness of their own or witnessing it in someone they care about could lead to symptoms of depression in a teen. A teen may feel like illness is constantly on their mind, affecting how they sleep, eat, concentrate, and spend time with friends. For instance, studies have shown that having a parent with an illness such as cancer can make a teen feel constantly worried and distressed. They may feel scared and unable to turn to their usual support systems, such as family and friends, for advice and comfort.1,2