According to FleaBites.net, bites from fleas typically require a few weeks to fully heal. The time it takes for flea bites to heal is heavily dependent on how sensitive a person is to them.
FleaBites.net explains that seeking treatment can cut the amount of time it takes to heal from one or more flea bites. DermNet NZ also explains that scratching flea bites can cause them to become red and inflamed, resulting in an even longer recovery time since the skin is still irritated. The website also warns that a secondary infection can develop from the excessive scratching of flea bites.