New York City is cracking down on Airbnbs. It’s already illegal to rent out an entire apartment or house for less than 30 days, though you can still rent out a room in your apartment for short stays, as long as you’re home at the time.

But starting Sept. 5, the city will enforce the law more aggressively. A big part of the reason is concern that the explosion in short-term rentals has exacerbated the affordable-housing crisis.

So, how much do short-term rentals affect long-term rentals?

New York City did a study five years ago that found the more Airbnbs there are in a neighborhood, the higher rents go.

“For every 1% increase in Airbnb rentals, it was a 1.6% increase in long-term rental rates,” said Jaime Peters at Maryville University.

While that may not sound like much, “it adds up over time is the problem,” she said.

But while Airbnbs are clearly affecting the long-term rental market in some cities and towns, “there are other places where there is no evidence that it has much of an impact,” noted Richard Green at the University of Southern California.

In some cases, he said, short-term rentals can help people afford their rent or their mortgage.

“Suppose there’s a flight attendant who’s out of town a lot. He may decide to rent out his apartment while he’s not there, which is a way that it makes it more affordable for him to live in a place like New York City,” Green said.

Ultimately, while short-term rentals contribute to the affordability problem in some places, Green added that the bigger issue is there just isn’t enough housing. Period.