E-cigarettes don’t contain tobacco and don’t burn, so breath tests that look for carbon monoxide may be negative. But urine, blood, and saliva tests that look for the chemical cotinine will be positive. Cotinine appears when nicotine is broken down in the body, and e-cigarettes contain nicotine, just like the nicotine patch or gum.
Medical review: Nathan Cobb, MD, September 12, 2017