Last fall, in Airbnb’s first major advertising campaign in more than two years, it portrayed hosts as regular homeowners happy to rent out a spare room and socialize with their guests. The message—that Airbnb helps foster a global community by bringing together travelers and locals—is one Airbnb has promoted since its earliest days.

While these so-called amateur hosts still dominate Airbnb’s listings, their share of the total appears to be shrinking as full-time rental properties expand rapidly. The number of Airbnb listings likely to be operated by hospitality professionals grew 36% last year, more than three times the increase in listings for rentals of spare rooms, according to previously unreported data from AirDNA, which analyzes short-term rental sites. 

The slower growth of more-casual hosts has worried some Airbnb executives, who see those listings as a way to distinguish the brand from rivals like Booking.com and Vrbo. They have another reason to be anxious: The professionally run properties that are the source of the company’s strongest growth have faced intense regulatory pushback in the last few years. Major cities including Los Angeles, New York, Paris, London and San Francisco have capped the number of nights that hosts can rent their homes on Airbnb, though some of the cities struggle to enforce the restrictions.