By the time I was 25 it had developed into a fear that I would harm the people I loved, particularly the young and vulnerable. I know it seems mad that I have done this column for so long without admitting any of this, but at times my OCD has seemed so shameful I haven’t been able to write about it. Because when people think of OCD, they think of hand-washing and cleanliness and order; no one ever talks about “Pure O”, an incredibly common, but little-known, form of the illness that makes people obsess over intrusive thoughts about blasphemy, abuse, sex, even murder. While most people have occasional weird thoughts but let them go, the person with Pure O feels such discomfort at such thoughts that they obsess until they become convinced they must be a potential serial killer or stalker or paedophile.