Those who suffer from SAD during the winter months are reported as having many of the same signs as an individual diagnosed with depression. These common symptoms include feelings of sadness, anxiety, irritability, loss of interest and/or pleasure in the individual's usual activities, withdrawal from social activities, and inability to concentrate. Out of the individuals who are diagnosed, research indicates that 75 percent are women with the majority being in their 20s to 40s. SAD can also occur in children and adolescents, but older adults are less likely to experience all of the symptoms of SAD.

There can be a number of reasons an individual may experience SAD, including where an individual lives and even their body chemistry. SAD is seen more commonly in individuals who live at high latitudes, which can be explained due to more extreme seasonal changes. As for body chemistry, it is suggested that individuals who suffer from SAD, may have an alteration to the neurotransmitters dopamine and serotonin. When either are not properly synthesized within the body they can have physiological effects on a person such as SAD. Dopamine has many functions within the brain. The important roles that dopamine plays can affect an individual's sleep patterns, motivation, mood, appetite, and even attention. Serotonin performs many significant tasks that include but are not limited to, regulating mood, appetite, and sleep patterns.

In order to explain the turnaround in the warmer months, one needs to understand the relationship between SAD and light. It is believed that exposure to light can correct these imbalances. SAD is traditionally treated with light treatment, antidepressants, or even a combination of the two. Spending time outdoors during the day has also been stated to be helpful. Melatonin is the reason that an increase in light exposure is deemed necessary if experiencing depressive symptoms. Melatonin is a hormone that is secreted by the pineal gland located in the brain. It is believed to regulate the sleep-wake cycle in humans producing sleepiness and decreasing an individual's body temperature. By exposing oneself to increased light, an individual would be inhibiting the production of Melatonin, which is thought to help with managing depressive symptoms.