Rendered from animal fat, tallow or lard is commonly used as an ingredient in soaps. It is produced from the kidneys and loins of cattle, horses and sheep. Tallow has been used for centuries, but experts are now saying that healthier alternatives exist, but they come with a higher price. Tallow has been proven to clog pores and cause blackheads and even eczema. This is because they are highly saturated. For this reason, products for cleaning skin and faces are starting to use detergents instead of soaps to achieve more "desirable properties." The detergents are softer on skin yet they still have comparable cleaning abilities.
Oil vs. Fat
There is no clear distinction between a fat and an oil. However, an oil is usually a liquid at standard temperatures, it will "flow", it is a lubricant and it is a fairly thick fluid. Fat generally entails a substance that is greasy, solid at room temperatures and is "slippery".
One thing that does set them apart, is in soap making. Tallow is often claimed to yield a harder soap than vegetable oils. It is also said that harder soaps are more "economical" and longer-lasting. Vegetable oil can only produce the same results when the combinations of oils are in accurate proportions and ratios. However, a result of these meticulously calculated and followed proportions of oil, is a very hard bar that does not melt in the soap dish and lasts just as long as a bar made from tallow.
Though both fats and oils can be used to make soap, not all oils will work. Hydrocarbon, otherwise known as a petroleum-based oils do not contain fatty acids and therefore cannot be used to make traditional soaps. However, animal and vegetable-based oils and fats can be used to make soap because they do contain fatty acids.