Boils

Which three makkos were not life-threatening?

The Ramban says that the makkos of Lice, Boils, and Darkness did not come with a prior warning to Pharaoh about the impending plague about to transpire. The reason was that these three makkos were not life-threatening, and therefore they did not warrant a warning.

According to the Ralbag, it is entirely likely that Pharaoh was warned, even though no warning is recorded in the pesukim (see 8:12 and 9:8).