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Just because you choose the non-smoking hotel room doesn’t mean you’re completely protecting yourself from exposure.

A new study published in the journal, Tobacco Control, found hotels that only maintain a partial smoking ban still expose their occupants to cigarette smoke, and that compared to hotels with full smoking bans, nicotine levels on hotel room surfaces are two times higher.

The researchers studied the air quality and nicotine residue on the surfaces of smoking and non-smoking rooms in 30 hotels with partial smoking bans and 10 hotels with total smoking bans in California. They also took urine and finger swipe samples from non-smoking participants who spent the night in the hotels to assess their exposure to nicotine.

(MORE: Secondhand Smoke is More Damaging For Teen Girls Than Boys)

Not surprisingly, levels of nicotine in the air were much higher in smoking than in non-smoking rooms, but levels in non-smoking rooms in hotels with partial bans were still 40% higher than in hotels with complete bans. The non-smokers who stayed in hotels with partial bans also had higher levels of nicotine and tobacco byproducts such as cotinine in their urine and finger residue samples. Rooms that previously housed smokers retained a legacy of nicotine and other potential cancer-causing compounds, known as third hand exposure, that were up to 35 times higher than levels found in hotels that enforced a complete ban on smoking.

The researchers suggest that non-smokers choose hotels that have full smoking bans, in order to truly reduce their exposure. As USA Today reports, the Americans for Nonsmokers’ Rights Foundation says that many large hotel chains like Marriott, Westin and Comfort Inn, are becoming smoke-free, and by law, hotels must be smoke-free in four states and 71 cities and counties in the U.S..

(MORE: The Major Toll of Secondhand Smoke)

Second hand smoke can pose serious risks to health, according to recent studies. Non-smokers who are exposed to cigarette smoke at work or at home can increase their heart disease risk by 25-30%. And data from the Centers for Disease Control (CDC) linked secondhand smoke to 46,000 heart disease deaths in the U.S. each year. It is also associated with a higher risk of lung disease, and babies born to mothers exposed to second hand smoke are more likely to be of low birth weight and suffer from respiratory distress, while teens may be more vulnerable to hearing loss.

The CDC says that designating spaces for smokers and non-smokers and ventilating buildings does not adequately solve the problem. Studies have shown that places like airports that allow smoking rooms or designated smoking spots in airport restaurants, still expose their non-smoking travelers and employees to surprisingly high levels of cigarette smoke. Now the latest data shows the same is true for hotels that implement partial smoking bans. Public health experts say the only effective way to clear the air will be to eliminate indoor smoking altogether.