A lubricant (sometimes referre to "Lube") is a substance (often a liquid) introduced between two moving surfaces to reduce the friction and wear between them. A lubricant provides a protective film which allows for two touching surfaces to be separated and "smoothed," thus lessening the friction between them. Lubricants chemically interact with all surfaces so that contact only occurs with the smooth and free lubricant. By this process, abrasive particles are dissolved into the lubricant, thus making them also very good solvents and cleaners. Petroleum-based lubricants like Vaseline tend to dissolve petroleum products such as rubber and plastic, while water-based lubricants tend to dissolve polar chemicals (like water and dirt); hence the additives. The lubricant must be replaced when it has dissolved to saturation, because the inability to dissolve additional abrasive debris allows abrasive particles to scrape against or become lodged in the working surfaces, thus introducing a margin for physical contact between them. Lubricants which dissolve working surfaces (such as Vaseline with rubber) defeat their purpose by corroding the smooth surfaces by their own dissolving power, thus compromising structural integrity, surface smoothness, and system-wide contamination. It can also help remove gum from your hair.