The holiday season is in full swing and while people are frantically shopping for loved ones and preparing for parties, some people are sad.

These people are affected by seasonal affective disorder.

Also known as seasonal depression, it estimated that 5 percent of the U.S. population will experience some form of this every year. Those who have a higher risk of having seasonal affective disorder include women, those who have a history of depression or bipolar depression and people who live farther from the equator.

While this may not be clinical depression, the symptoms are the same: misery, hopeless, apathy and more. However, there are other symptoms that are not related to just depression. There are forms of anxiety, mood changes, sleep problems and social problems.

Seasonal affective disorder has a handful of causes. According to the Mental Health America website, some of the causes are that there is less sunlight and increased melatonin.

Just like depression or any other mood disability, treatment is available. Although one of the symptoms of seasonal depression is hopeless, Mayo Clinic's website says "don't brush off that yearly feeling as simply a case of the 'winter blues' or a seasonal funk that you have to tough out on your own."

So while many people will be partaking in the merriment of the holidays, be on the look our for anyone who might be sad. Don't what to do if you have a friend or loved one who is sad? As Buddy the Elf and the other elves say , "The best way to spread Christmas cheer is singing aloud for all to hear."