The phrase “five o'clock shadow” is an English idiom referring to the appearance of a beard on a man’s face. The expression comes from the fact that many clean-shaven men will grow a slight stubble of beard on their faces by late afternoon or early evening. The slight growth of beard typically shows up by the end of the work day, around five o’clock, and looks a bit like a shadow on the man’s face, though when it appears varies greatly by individual.
An idiom is a phrase that is not meant to be taken literally. A five o'clock shadow is neither an actual shadow, nor does it necessarily appear just at five o’clock, but instead is used to indicate that a man has a day’s growth of beard, or looks like he needs a shave. Idioms such as this are commonly used, and most of the time people use them without even thinking about them. For non-native English speakers, this can add a level of confusion as they struggle to comprehend just what is being said. Not meant to be taken at face value, idioms add expression and color to the English language.
A five o'clock shadow appears on a man's face as facial hair grows throughout the day. Typically, a man shaves in the morning. Hair continues to grow throughout the day at different rates. By the end of the work day, usually considered five o'clock, many men will have stubble that appears as a shadow on the face.
The term “five o'clock shadow” originated in the 1930s, when it was coined for use in advertising designed to sell razor blades. The GEM® Razor Blade Company wanted to convince men that they needed to use only Gem razor blades for shaving in order to get the best and cleanest shave possible. The company created an advertising campaign that played on the horrors of a man being caught with a five o'clock shadow on his face. If a man was going to be presentable at the end of the day, he must shave with the best possible blades in the morning so that his beard would remain gone all day, and he would not suffer the humiliation of being caught with a five o'clock shadow on his face by evening.