Mineral oil is clear, odorless liquid that comes from petroleum. When petroleum is distilled from crude oil to make gasoline, mineral oil is also produced. Mineral oil has a variety of uses both industrially and in the food and cosmetic industries. It's an ingredient favored by manufacturers since it can be produced inexpensively in large quantities and has a long shelf-life.
Industrially, mineral is used as a coolant, an insulator and as a hydraulic fluid and cutting fluid. It also has applications in the veterinary field where it's used in the beekeeping industry and in livestock vaccines. Food grade mineral oil is also used as a protective coating for wooden bowls, utensils and cutting boards because of its ability to repel water. It can be rubbed on to cookware to keep food debris from sticking to pots and pans, making them easier to clean. It's also used to finish wood and polish certain surfaces to make them more water resistant.
Food grade mineral oil has a laxative effect, which is why you don't find it in large quantities in food products. Small amounts are sometimes used in candy products to keep the pieces from sticking together and to the packaging. The U.S. Food and Drug Administration allows mineral to be used in small quantities in food products like confectionary products. Food grade mineral is also used orally as a laxative.
Mineral oil is also an ingredient in some cosmetic and personal care products. Just as mineral oil serves as a protective coating for wood products, it also forms a protective layer over the surface of the skin to help reduce water loss. Mineral oil is one of the best examples of an occlusive moisturizer, one that coats and seals in moisture. It's so effective that it's often used as the "gold standard" by which other moisturizing ingredients are compared.
Mineral oil is also added to some commercial cleansing products due to its ability to dissolve oil and oil-based makeup. Some cosmetic and personal care products that may contain mineral include facial and body moisturizers, eye makeup removers, foundation, lipsticks, lip gloss and eye shadow.
As a product that comes from petroleum, some people are concerned about the safety of products that contain mineral oil. Mineral oil used in cosmetic and personal care products is highly refined and purified and has to meet certain safety standards before it can be used in products that are applied to the skin. It doesn't contain impurities that are found in mineral oil used industrially.
One advantage to mineral oil is it forms a barrier against moisture loss, but some studies suggest it's comedogenic, which makes it potentially problematic for people with oily or acne-prone skin, but more recent research suggests that mineral oil may not be as comedogenic as originally thought. Some people still think it feels "heavy" and oily when they apply it to their skin. Mineral oil isn't a photosensitizer isn't known to be allergenic and is unlikely to cause irritation in people with sensitive skin.
All in all, mineral oil appears to be safe in the quantities found in cosmetic and skin care products. Confusion as to its safety arises from the idea that all mineral oil is the same, but mineral oil used in food and cosmetic applications has undergone a more rigorous purification process to remove aromatic hydrocarbons that have been linked with an increased cancer risk. Mineral oil is one of the least expensive lubricants and moisturizers and one that hasn't been linked with allergies or skin irritation. Despite its safety in cosmetic products, it's not biodegradable and, therefore, isn't an environmentally-friendly ingredient. That's why you don't typically see it in products that are marketed as natural or organic.
For people who can look past the fact that it comes from petroleum, although it's highly purified, and the fact that it's not biodegradable, mineral oil is an effective solvent for removing oil-based makeup and a low-cost moisturizing ingredient. That's why it's still commonly used in cosmetic and personal care products despite misconceptions about its safety.