The phrase "skin-deep" refers to something that is superficial, only affecting the surface and lacking depth or substance. Common synonyms for "skin-deep" include shallow, surface-level, superficial, and cosmetic. Other related words include external, appearance-based, and fleeting. While these words all describe the same general idea, they can be used in different contexts to convey varying levels of severity or meaning. For example, "superficial" may imply a lack of emotional depth or insight, while "cosmetic" specifically relates to appearance-based treatments or enhancements. No matter which word is chosen, they all describe something that lacks true depth or meaning.