Forget free wine hours and on-demand workout videos. An increasing number of hotels around the world are now providing guests the option to book rooms with filtration and purification systems that minimize threats of air pollution and offer cleaner air.

“Interior air quality can be abysmal,” said Beth McGroarty, research director for The Global Wellness Institute, a nonprofit organization for the wellness industry. “Hotels are combating this by installing high-tech systems in some of their rooms that improve the air their guests are breathing.” The quest for clean air is part of the growing interest in wellness travel, McGroarty said.

Outside conditions could certainly be a larger factor. According to data released last year by the World Health Organization, 9 of 10 people globally breathe polluted air. Many top urban destinations, particularly in developing nations, have been recognized for unhealthy smog conditions. Wildfires are becoming more frequent, affecting the air quality of hundreds of miles. And travelers with respiratory conditions or allergies may especially benefit from breathing cleaner air.

Most hotel properties generally charge a higher nightly rate for their clean air rooms, compared with their standard rooms, and while the amount varies depending on the hotel, a stay can be 5 to 7 percent more expensive.

In January, the 556-room InterContinental San Francisco installed Molekule air purifiers in 30 of its rooms as part of a pilot project. According to Molekule’s chief executive, Dilip Goswami, the 2-foot tall, cylindrical devices plug into a power outlet and eliminate mold, bacteria, chemicals, allergens and viruses through the company’s patented air purification technology.

The hotel wellness company Pure Wellness has designed “Pure Rooms,” available in 300 hotels globally and spanning several companies including Marriott, Hampton Inn, Embassy Suites and Hyatt. Pure Rooms are guest rooms that are deep cleaned with plant-based and microbial-­resistant cleaners, developed to prevent the growth of fungus, bacteria and mold.

The wellness technology company Delos is behind the “Stay Well” designation of more than 1,000 hotel rooms found globally, including those in Wyndham, Marriott and MGM Grand hotels. One of their key features is a wall-mounted air-purification filter that aims to reduce allergens and microbes. For Wyndham’s 50 hotels in North America, the rooms are now a brand standard.