'Doubles your risk' could mean 1 in a million to 2 in a million. Always ask: out of how many?
Example
If lifetime risk of a disease is 5% and a habit raises it 18%, the new risk is about 5.9% — under 1 extra case per 100 people.
Evidence & sources
People understand risks better when they are shown as absolute numbers ('2 in 1,000') rather than only relative changes. Evidence: established. Known: Review of risk-communication research. Unknown: — Source: US FDA, Communicating Risks and Benefits: An Evidence-Based User's Guide (2011).