To outsiders depression can be difficult to understand. It's more than just sadness or a bad day, it's a medical illness that can affect personal relationships, work and even interests.

"It's different than feeling down or blue," said Dr. Michael Ziffra, a psychiatrist and assistant professor of psychiatry and behavioral sciences at Northwestern University Feinberg School of Medicine. "When one is depressed, there will be definite changes in function that they will notice."

The duration also distinguishes depression. Feeling sad might last a day or two, but depression can last weeks, months or even years.

But just because someone is suffering a bout of depression, it no longer has to affect their lives in ways that make it unmanageable. It can be managed, and for those that are lucky it might get better with time.

What is depression?

Depression is an illness that affects the way someone feels, acts and behaves. It's not something that someone can "snap out of" and it's more than sadness over a day's events. Generally it is considered a long-term illness and requires treatment to get better.

According to the Mayo Clinic, symptoms including a feeling of sadness, irritability or frustration even over small matters, a lack of interest in usual activities, slowed thinking, indecisiveness, restlessness, fatigue, feelings of worthlessness, crying spells and thoughts of suicide.

Some patients with depression also may have trouble sleeping, notice a reduced sex drive, have a change in appetite and even unexplained physical problems such as back pain and headaches, though symptoms tend to vary depending on the person.

The exact cause of depression hasn't been pinpointed, but in some cases may relate to genetics, some kind of trauma or life event, hormones or brain changes or chemistry. Most often depression starts while someone is in their early 20s, but it can happen at any age, according to the Mayo Clinic. The teenage years are another period when the disease often manifests itself.

"There are special factors that make teenagers more at risk," said Dr. Ziffra. "Evidence seems to suggest that the earlier in life someone has an episode of depression, the more likely it will be recurrent, and the more likely it will be severe."

Some patients wait to get treated, initially believing they are just sad or down, and it is not uncommon for them to report prior undiagnosed episodes of depression. Dr. Ziffra said that sometimes it is found that "some people have been struggling for years."

"People wait a little bit. Partially it is the stigma of seeking mental health treatment," said Dr. Ziffra. "They think they can fix it on their own or that it will get better with time. Or they might be turning to drugs and alcohol. It's not uncommon that someone will experience symptoms for months or years before seeking treatment."

Those most at risk have a family history of depression, alcoholism, suicide; or abuse drugs. A serious illness or stressful life event or certain personality traits such as low self esteem also can cause depression. Women also are believed to suffer from depression at higher rates than men.

Treatments for depression

There are treatment options for depression, with the most popular being talk therapy and medication. Some do one or the other, but utilizing both treatments tends to lead to more success for patients.

Antidepressants are the primary medication prescribed. Many new ones have been introduced in recent years but there haven't been substantial changes in medication since the late 1980s when selective serotonin reuptake inhibitors (SSRIs) such as Prozac were introduced. Other SSRIs include Celexa, Zoloft and Paxil.

Other drugs prescribed include serotonin and norepinephrine reuptake inhibitors such as Cymbalta, norepinephrine and dopamine reuptake inhibitors such as Wellbutrin and tricyclic drugs, a class of older medications believed to be as effective as newer drugs.

"Every few years new antidepressants come out. Many are not that different, but the ones in the last 10 to 20 years have gotten much better," said Dr. Ziffra. "And the general side effects are not too bothersome. If the side effects are hard to manage, we can always switch medication."

Though drugs can help manage the symptoms, the medication is generally viewed as longer term assistance. Dr. Ziffra said it is usually recommended that patients take the medication for at least several months even if they feel better sooner.

"If they stop taking medication too soon, it can be associated with increased relapse," he said. "If it gets to the point where a person wants to come off medication, we want to make sure they have been symptom free for several months."