The Department of Health and Human Services (HHS), under the leadership of Robert F. Kennedy Jr., will define sex as an "immutable biological classification" and only recognize two sexes, male and female, according to guidance issued Wednesday.
The guidance builds on President Donald Trump's executive order that instructed the federal government to officially recognize only a person's sex at birth and to stop recognizing the concept of gender identity. The HHS released the guidance to the U.S. government, external partners and the public.
"The guidance recognizes there are only two sexes: male and female. HHS will use these definitions and promote policies acknowledging that women are biologically female and men are biologically male," officials said Wednesday in a press release issued by HHS.
RFK Jr. assumed his role as HHS secretary last week, and the guidance marks one of his first policy moves.
“This administration is bringing back common sense and restoring biological truth to the federal government,” RFK Jr. said in a statement. "The prior administration’s policy of trying to engineer gender ideology into every aspect of public life is over.”
The HHS also launched a new web page, called "Protecting women and children," that links to Trump's executive orders aimed at transgender people, including orders that seek to stop gender-affirming care for minors and keep transgender women and girls out of female sports.
The guidance lays out definitions the HHS will use, including that sex is a "person’s immutable biological classification as either male or female" and defines "father" as a male patient and "mother" as a female patient.
A female is defined as a "person of the sex characterized by a reproductive system with the biological function of producing eggs (ova)" and a male is defined as a "person of the sex characterized by a reproductive system with the biological function of producing sperm," according to the HHS guidance.
A woman is "an adult human female" and a man is an "adult human male," the guidance instructs.
“In health care, sex distinctions can influence disease presentation, diagnosis, and treatment differently in females and males,” said Dorothy Fink, M.D., deputy assistant secretary for women’s health, in a statement. “HHS recognizes that biological differences between females and males require sex-specific practices in medicine and research to ensure optimal health outcomes.”
In the U.S., 1.6 million people over the age of 13 identify as transgender. Many scientists and medical experts say the scientific understanding of sex extends beyond a simple binary (male/female) model.
The American Academy of Pediatrics is one medical organization that recognizes not everyone fits into the narrow definitions of male or female. It defines gender identify as "one's internal sense of who one is, based on an interaction of biological traits, developmental influences, and environmental conditions. This may be male, female, somewhere in between, a combination of both or neither. Self-recognition of gender identity develops over time, much the same way a child's physical body does," the medical organization wrote.
In a fact sheet released this month, the American Society for Reproductive Medicine wrote that legislation and proposals "to define sex into two easily determined categories are unsupported by science and oversimplify the intricate nature of human biology."
"It is crucial to understand that biological sex is determined by biology, not politics," ASRM wrote.
The organization noted, "While XX and XY chromosomes are often associated with female and male sexes, variations such as XXY, XYY, and others also occur in an estimated 1 in 1,500 to 1 in 2,000 live births, which amounts to approximately 200,000 to 330,000 Americans based on the current population.
It is not uncommon, ASRM points out, for individuals to have atypical combinations of chromosomes, hormones, or anatomy, challenging the binary model of sex assignment. "Such natural variation, which is neither a disease nor a disorder requiring medical intervention, i lustrates the complexity of biological sex," ASRM wrote.
For example, Kleinfelter syndrome is a common condition that results when a person assigned male at birth has an extra copy of the X chromosome instead of the typical XY.
Major medical groups also support gender-affirming care for transgender individuals, which is comprised of a range of social, behavioral and medical interventions, the latter of which include puberty-blocking medications, hormone treatments and, in rarer cases, surgical procedures.
Trump has issued several orders that target the trans community, as KFF reported. He has directed his administration to recognize only the male and female sexes—and to abandon the term “gender” altogether. He ordered the State Department to issue passports identifying Americans only by their genders assigned at birth. He has encouraged the Justice Department to prosecute teachers and other school officials who help trans children transition, including by using their preferred names. And he signed an order that’s expected to lead to transgender people being banned from military service.