Body odor or body odour (BO) is the unique odor secreted by an animal or produced by microorganisms on an animal's outermost surfaces. It is present in all animals, and its intensity can be influenced by many factors. Body odor has a strong genetic basis, but it can also be strongly influenced by various factors, such as sex, diet, health, and medication. The body odor of human males plays an important role in human sexual attraction as a powerful indicator of genetic variation ; significant evidence suggests that women are attracted to men whose body odor is different from theirs, indicating that they have immune genes that are different from their own, which may produce healthier offspring.