'Doubles your risk' can mean going from 1 in a million to 2 in a million. Always ask: risk of what, out of how many?
Example
If 2 in 100 people get a disease and a habit raises it 18%, that's about 2.4 in 100 — 0.4 more people per 100.
Evidence & sources
Presenting risks as absolute numbers helps people understand them better than relative risks alone. Evidence: strong. Known: Risk communication research. Unknown: — Source: US FDA, Communicating Risks and Benefits: An Evidence-Based User's Guide (2011).