Germ-free, or GF, animals are laboratory animals that completely lack microbes, making them useful tools for microbiome research. Researchers create GF animals in laboratories by delivering the newborn animals in a way that protects them from microbes, which are microscopic organisms such as bacteria and viruses. They then house the GF animals in sterile conditions to ensure that the animals stay germ free. The creation of GF animals began in the late nineteenth century. Prior to that, scientists had no way to study the effects of the microbiome on overall health. The creation of GF animals allowed researchers to examine the microbiome under controlled conditions. They could colonize the animal with specific microbes and study their effects on the animal’s health without the confounding presence of other microbes. Researchers have used GF animals as a living model to study the microbiome, which has provided evidence for a relationship between the microbiome and health, including a role for the microbiome in shaping the development of multiple body systems.

Metoidioplasty is a type of gender-affirming surgery that creates a small-sized neophallus, or new penis, from an enlarged clitoris. Gender-affirmation surgeries are procedures that alter a person’s body, typically sexual characteristics like the genitals, to align a person’s sex with their gender identity so that they can move through society more comfortably. Such procedures treat gender dysphoria, which is the distress or discomfort that may be felt by transgender people. Transgender people’s gender identities differ from the genders they were assigned at birth, usually conflated with the sex they were assigned at birth. As opposed to a phalloplasty, a procedure where a neophallus is created using tissue from other areas of the body and not just the existing genital tissues, metoidioplasty allows transgender individuals to have a penis with less noticeable scarring, preservation of erogenous sensation, and, if the patient desires, the ability to urinate while standing. The technique was first suggested in 1973, then performed in 1974, however, doctors and researchers did not refer to it as metoidioplasty until 1989. Since its implementation, several modifications have ensured lower risks and better results for patients. Metoidioplasty improves the quality of life for people seeking gender-affirmation surgery by treating gender dysphoria.

The DTaP vaccination series is an FDA-approved, five-shot vaccine for young children in the United States for protection against diphtheria, tetanus, and pertussis. DTaP stands for diphtheria, tetanus, and acellular pertussis, which are all common childhood diseases. In the US, Daptacel and Infanrix are the two types of DTaP vaccines, whereas other countries offer other variations. Both Daptacel and Infanrix consist of five shots that stimulate the immune system to protect a child against those diseases. Children vaccinated with DTaP may still end up getting one of the diseases, but they often present with milder symptoms than if they were not vaccinated. The general vaccination schedule for the five shot series is two months, four months, six months, fifteen to eighteen months, and four to six years of age. DTaP vaccination fully protects nine out of ten children against acquiring disease, contributing to a downward trend in diphtheria, tetanus, and pertussis cases in developing children in the US.

Hormone replacement therapy, or HRT, is a form of medication often used to treat the symptoms of menopause. According to the National Institute on Aging, menopause is the point in a female’s life twelve months after she has had her last period. The time leading up to menopause, often called perimenopause, is a transition stage when levels of sex hormones, namely estrogen and progesterone, begin to fall. For approximately eighty-five percent of menopausal females, that decline results in symptoms such as vaginal dryness, shifting moods, and hot flashes, or an abrupt feeling of warmth typically in the upper body. HRT replenishes a person’s sex hormones, and though there are many methods of HRT, people most commonly take a pill that contains either estrogen only or both estrogen and progesterone. HRT has evolved scientifically but has at times resulted in controversy over potential side effects. Despite historical controversy, as of 2024, researchers recognize that with careful consideration of an individual's health conditions and history, HRT can be an effective treatment for menopausal symptoms.

In 2021, the World Health Organization, or WHO, published the sixth edition of their Laboratory Manual for the Examination and Processing of Human Semen, which provides standardized guidelines to physicians and other medical professionals performing semen analysis. Semen analysis is a technique that medical professionals use to analyze the characteristics of a male’s semen and sperm cells to identify possible causes of male infertility. A sperm cell is the male sex cell that fertilizes a female’s egg cell, while semen is the fluid containing sperm cells that men release during ejaculation. The WHO created the first laboratory manual for semen analysis in 1980, a time when there was no standardized way to analyze a male’s semen sample. The WHO laboratory manual was one of the first documents to standardize a procedure for evaluating human semen to look for sperm abnormalities, and it remains one of the most widespread methods of evaluating a male’s fertility potential and determining the causes of male infertility.