stylistic:tone, information:classification
Lambskin

Condoms made from sheep intestines, labeled "lambskin", are also available. Although they are generally effective as a contraceptive by blocking sperm, studies have found that they are less effective than latex in preventing the transmission of sexually transmitted infections because of pores in the material. This is because intestines, by their nature, are porous, permeable membranes, and while sperm are too large to pass through the pores, viruses—such as HIV, herpes, and genital warts —are small enough to pass.

As a result of laboratory data on condom porosity, in 1989, the FDA began requiring lambskin condom manufacturers to indicate that the products were not to be used for the prevention of sexually transmitted infections. The FDA cautions that while lambskin condoms "provide good birth control and a varying degree of protection against some, but not all, sexually transmitted diseases", people do not know what STIs a partner might have, and thus cannot assume that a lambskin condom will protect them.

While lambskin condoms avoid triggering latex allergies, polyurethane condoms do as well, while also protecting more reliably against STIs. As slaughter by-products, lambskin condoms are also not vegetarian. Pharmacist advice prepared by the Canadian Pharmaceutical Journal says that lambskin condoms "are generally not recommended" due to limited STI prevention. An article in Adolescent Medicine advises that they "should be used only for pregnancy prevention".