You can start a sentence with “especially.” However, in formal writing, it is not common to do so, and you should avoid it in academic writing. In informal English, it is more common to begin a sentence with “especially.” E.g., “Especially because I’m married, I have little free time.”

The basic rule is simple: If especially starts a sentence or is part of a non-restrictive clause, it should be followed by a comma. For example, “Especially in the winter, the roads are slippery.” Here, the comma after especially sets off an introductory phrase.