Mold generally prefers higher humidity levels, but it can grow at lower levels as well. So, while 55% humidity isn't ideal for mold growth, it's certainly possible that mold could start to grow in your home if the conditions are right. To prevent mold growth, it's important to keep your home's humidity level below 60%. You can do this by using a dehumidifier or by opening up windows and doors to let fresh air in. If you suspect that there is already mold growing in your home, it's important to have it professionally removed as soon as possible.