In simplified words, depression can be defined as sadness or grief that persists for excessively long duration as compared to normal and significantly impairs the normal functioning of an individual.

On account of millions of people being affected by depression worldwide, it is a huge public health problem. It is especially important to diagnose it and treat it in time because it affects not only the patient but his entire family as well as his work.

Depression can affect people of all ages and backgrounds; females are twice as likely to suffer from it as compared to males. The major problem with this condition is that it often presents with sub-clinical symptoms leading it to be under-diagnosed and hence under-treated.

The condition has a propensity to worsen as time progresses and it can substantially affect the functionality of an individual. In the worst scenario, depression can lead to suicide which results in loss of as many as 850,000 lives every year.

A few decades ago, depression would be classified as:

Endogenous: This type is described as one in which there is no external cause for the depression; it can be of genetic origin or may be idiopathic.

Neurotic / reactive: This type has an obvious external factor that has precipitated the condition. Common triggers include loss of a loved one, end of a relationship, death of spouse, a major set-back in life, etc.

Currently, depression is broadly classified into the following types, the first two being the most commonly diagnosed ones:

Major depression: This significantly disables the sufferer and prevents him from functioning normally. It interferes with a person's ability to enjoy activities which he once found pleasurable. Major depression can become recurrent or chronic in nature.

Chronic depression (dysthymia): Longer duration (usually more than 2 years) but less severe symptoms characterize this type. It is less disabling as compared to major depression.

Bipolar depression: Also called manic-depressive illness, patients suffering from this type have episodes of extreme highs (like mania) alternating with extreme lows (like depression). This condition tends to be cyclic in nature.

Seasonal depression (SAD or seasonal affective disorder): Typically, the patient experiences episodes of depression during the winter months (when there is less natural sunlight) and this gets better with the onset of spring / summer.

Psychotic depression: When depression is accompanied by the patient getting away from reality and experiencing delusions / hallucinations, it's called psychotic depression.

Postpartum depression: The onset of major depression within a month of delivering a baby is called postpartum depression and it affects almost 10-15% of women.