Under the skin is a phrase that represents the deeper part of something or someone. It is usually used to refer to a feeling or knowledge that is not expressed overtly. Synonyms for under the skin include beneath the surface, deep-seated, ingrained, internalized, and hidden. Each of these phrases encapsulates the idea that there is something hidden in a person or situation that requires close examination to be discovered. For example, when we say that someone's behavior is getting under our skin, we are referring to their actions affecting us on a deeper level, rather than just being an annoyance. These synonyms help us understand and describe this complex concept.