f you've ever been rejected by an insurance company, there's good news: starting January 1, you won't have to go uncovered any longer.

When Shana Alex Lavarreda, now 37, had just graduated from college, she tried to buy health insurance on her own. Surprisingly, she was rejected. Why would a 22-year-old young woman in perfectly good health be rejected by an insurance company? Simply because she had once seen a doctor for back pain.

But now, starting in January, because of the Affordable Care Act, insurers will be prohibited from using pre-existing conditions as a reason for exclusion, and people with diseases such as cancer or diabetes, or health issues such as the back problems Shana had, won't have to pay a higher premium. The only factors that will now determine how much a person pays are age (older people pay up to three times more), where you live (varies by state and county) and in some states, whether you smoke.

The reason insurers currently reject about one in five applicants trying to buy coverage is that they are considered too high a medical risk, estimates the U.S. Department of Health and Human Services. This estimate does not include the number of people who are given higher rates because of a pre-existing condition.

To help protect insurers from major losses when they can’t reject people with medical problems, the health law mandates that most people, including millions of healthy young people, get insurance.

Megan Ford, 27, of St. Louis, says she has been turned down by every major health insurer because of her epilepsy, and an autoimmune disease that causes nerve and muscle pain as well as fatigue. Ford once ran her own public relations business but when she could not find individual coverage, she took an administrative job at a hospital to help her get health insurance (pre-existing condition exclusions don’t impact people getting coverage at work). She was laid off in September. She is looking forward to now buying coverage without concern about her health problems. “This is a big weight off my shoulders.”

Olivia Grey Pritchard, 32, a freelance photographer in New Orleans, was turned down by several insurers in 2011. The reason? She took Accutane for acne as a teen and had a benign tumor removed when she was 23. For the past year, she’s been covered by the health law’s Pre-Existing Condition Insurance Plan, which ends December 31. Pritchard looks forward to shopping for plans without worrying about being rejected.

Shana Lavarreda, now director of health insurance studies at the UCLA, says the upcoming change will benefit millions of young women. “Without [worrying about] pre-existing conditions, you can really shop around and have much more freedom, knowing they can’t refuse you.”

“This is something that every American is entitled to,” adds Pritchard. “This is not a gift. This is correcting a wrong.”

Cosmo tip: If you don't receive health insurance through work, go to healthcare.gov by December 23 to shop around and sign up for coverage that will begin January 1, 2014. After that, you can continue to sign up until the end of March 2014. Past that date, if you don't sign up and remain uncovered, you could face a tax penalty, which would be either $95 or 1 percent of your household income, whichever is greater. You'd pay this when you file your 2014 income taxes; the penalty would be deducted from whatever refund you may be owed.