These animals breed rapidly and are inexpensive to feed and house. There are very few animals used for cosmetic testing. Animals are only used in cosmetic testing when a new ingredient is developed.
Many companies advertise that their product has never been tested on animals.
This is misleading - all the ingredients in their products have been tested on animals at some time, and found to be safe. These companies did not necessarily do the testing themselves. Many diseases have been eliminated or controlled because of animal research. Animals are a very important part of vaccine development and testing. Without animal research, diseases like smallpox could not have been wiped out, and polio, whooping cough, tetanus, and measles would be much more common.