It doesn't discriminate, touching the lives of people in every corner of society - from the homeless and unemployed to builders and doctors, reality stars and footballers.
It's the biggest killer of people under the age of 35, more deadly than cancer and car crashes.
And men are three times more likely to take their own life than women.
Yet it's rarely spoken of, a taboo that threatens to continue its deadly rampage unless we all stop and take notice, now.
That is why The Sun launched the You're Not Alone campaign.
The aim is that by sharing practical advice, raising awareness and breaking down the barriers people face when talking about their mental health, we can all do our bit to help save lives.
Let's all vow to ask for help when we need it, and listen out for others... You're Not Alone.
If you, or anyone you know, needs help dealing with mental health problems, the following organisations provide support:
- CALM, , 0800 585 858
- Heads Together,
- Mind, , 0300 123 3393
- Papyrus,, 0800 068 41 41
- Samaritans, , 116 123