Who hasn’t felt a lonely or sad at times? We all have days when we feel down, blah, or overwhelmed with life, and we may even go through periods when we have a really tough case of the blues. If we take a closer look, however, there’s often an identifiable cause behind those feelings; a loss, an emotional or physical blow of some kind.

Grief over the death of a loved one, the end of a relationship, the loss of a job, a financial setback, or some other type of extreme hardship may cause us to feel a bit hopeless and miserable temporarily. Having those feelings doesn’t necessarily mean we’re depressed—it might just be our normal and understandable reaction to life’s hardships.

So how do we know if we, or someone we care about, are suffering from depression rather than just ordinary sadness? It’s not always easy to tell the difference. The short, quick answer is that sadness is a temporary emotion, usually with a recognizable cause, while depression lasts for longer periods of time; sometimes forever, and often for no discernible reason. Perhaps the most important indicator of depression is that it interferes with the ability to lead a normal life.

Recognizing depression can be extremely difficult, and the quick definition oversimplifies a very complex problem. There are many signs of this condition that you may have not considered, and to make it even harder, the signs and symptoms vary greatly from person to person, as does the severity. Worse, it’s harder to notice the signs when you are in the midst of depression already, which is why other people often notice before the depressed individual does.

The warning signs are there, but knowing what to look for makes it much more likely that you will spot them sooner.