The number of public places where a smoker can light up is shrinking fast.

Exiled from most office buildings, restaurants and theaters, smoking is increasingly being banned even outside. During the past five years, the number of parks and public recreation areas that prohibit smoking has almost doubled to almost 2,600 nationwide, the Associated Press notes.

While there is evidence that second-hand smoke in a closed environment — like an office or restaurant — can produce health problems, some experts say there is little research documenting ill effects from inhaling smoke in the outdoors.

The lack of evidence hasn’t stopped lawmakers and anti-smoking advocates from pushing more more outdoor smoking bans. Federal health officials insist that even small amounts of inhaled cigarette smoke are dangerous. At least one study found that traces of smoke could be found up to 44 feet away from a cigarette smoker.

Of course, many non-smokers find cigarette smoke irritating and would like it banned in playgrounds and parks on that basis alone.

Regardless of the evidence, the move to prohibit smoking in public outdoor spaces is only likely to grow in coming years. Earlier this year, even Russia moved to outlaw smoking at public venues.

Restrictions on public smoking may also be driving rising sales of electronic cigarettes, which don’t produce smoke. Most cigarette makers including, Altria Group (MO), Lorillard (NYSE:LO) and Reynolds American (NYSE:RAI) are either testing or selling e-cigs.