It seems that cost-conscious millennials are so down on being in debt that many are avoiding credit cards altogether. But in doing so they’re missing out on the opportunity to start building a credit history, which is crucial for securing loans, renting apartments and getting the best insurance rates. These are the findings from a recent NerdWallet study, which reported that 31% of U.S. adults between the ages of 18 and 34 have never applied for any type of card. What’s more, 28% of these surveyed millennials had credit scores between 300 and 579, far below an optimal 700 that gets you the best lending rate from the banks. Bottom line: Using a credit card responsibly is one of the easiest ways to improve a low credit score.