Polyurethane is essentially a plastic that is liquid until it cures, is available in both water and oil-based versions, and comes in several finishes ranging from satin to glossy. Because of its low toxicity and minimal odor, water-based polyurethane is popular. It goes on clear and dries considerably faster than oil-based alternatives, plus it doesn’t add any color. Water-based polyurethane is susceptible to heat and chemicals. It’s ideal for bookcases, desktops, and picture frames that won’t be subjected to high temperatures. Oil-based polyurethane is more durable than water-based polyurethane, especially when it comes to heat resistance, therefore it’s a smart choice for a kitchen table. Although polyurethane is frequently confused with being different then wood sealer, it is actually a form of sealer.
Some can be, yes. Most molds cause allergies that are uncomfortable but not life-threatening. However, all can be dangerous for people with asthma, compromised immune systems, the young or the aged....
Yes. But you must ensure adequate ventilation around the wood, reduce moisture ingress, and preferably protect the surface of the wood. Regular dusting, vacuuming, and wiping down also help.