(Bloomberg) -- Healthier people will avoid buying Affordable Care Act health insurance plans aspremiums climb, threatening the stability of the market, Aetna CEO Mark Bertolini said.

“As the rates rise, the healthier people pull out because theout-of-pocket costs aren’t worth it,” Bertolini said at Bloomberg’sThe Year Ahead Summit in New York. “Young people can do the math.Gas for the car, beer on Fridays and Saturdays, healthinsurance.”

Premiums for health plans sold to individuals under the ACA,known as Obamacare, are going up by about 25 percent onaverage for next year. Bertolini said that as costs rise, moreindividuals will decide not to buy health plans. That’ll pushpremiums even higher, unless a new president and lawmakers can findfixes for the new markets created by the 2010 health law.

Related: Aetna: ACA exchange exit not politicallymotivated

“What happens is the population gets sicker and sicker andsicker and sicker,” Bertolini said. “The rates keep rising to tryand catch it. It’s a fruitless chase, and ultimately you end upwith a very bad pool of risk.”

The government has emphasized that subsidies are available formany people to help cushion the premium increases. When they aretaken into account, about 77 percent of current ACA enrollees willbe able to buy health insurance for $100 or less a month, the U.S.said in a report on Monday.

Insurer Aetna itself is largely ending sales of ACA plans,because it’s recording hundreds of millions of dollars of losses onthe policies. The insurer will offer individual coverage on theACA’s exchanges in four states for next year, down from 15.

Bertolini said Aetna would consider restarting sales on ACAexchanges if lawmakers make changes to the market that would helpplans bear the cost of enrollees who’ve turned out to be sickerthan expected. He also said passing laws will take time, given thereluctance of some legislators to improve the ACA.

Related: Insurers battle Republicans over ACAreinsurance program

“We have the ability to get back in to the exchanges if theregulation gets it right,” he said. “I don’t think that’s going tohappen any time soon enough for us to get back in before 2019,maybe 2020.”

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