A DSD athlete is a competitor who has a difference of sex development, a group of congenital conditions where chromosomal, gonadal, or anatomical sex develops in ways that don’t fit typical male or female patterns. The term comes up almost exclusively in women’s elite sports, where certain DSDs can result in naturally elevated testosterone levels, sparking ongoing debate about eligibility and fairness.
What “Differences of Sex Development” Means
Sex development has three major components: chromosomal sex (your combination of X and Y chromosomes), gonadal sex (whether you develop testes, ovaries, or both), and anatomical sex (your internal and external reproductive anatomy). In most people, these three components align in a predictable way. In people with a DSD, one or more of these components develops atypically.
DSDs cover a wide range of conditions. Some cause few outward differences and may go undetected for years. Others raise questions about anatomy, hormone levels, or fertility from birth. A person with a DSD may have XY chromosomes but develop female external anatomy, or may have both ovarian and testicular tissue. Many people with DSDs are raised as girls, identify as women, and only discover their condition through medical testing later in life, sometimes triggered by sports eligibility screening.
The Specific Conditions That Matter in Sports
Not every DSD is relevant to athletic regulation. World Athletics, the governing body for track and field, names a short list of conditions that trigger eligibility rules:
- 5-alpha reductase type 2 deficiency: The body produces testosterone but can’t fully convert it into its more potent form. People with this condition typically have XY chromosomes and internal testes but may develop female-appearing external anatomy.
- Partial androgen insensitivity syndrome (PAIS): The body’s cells partially respond to testosterone. Testosterone levels may be high, and the body uses some but not all of it.
- 17-beta hydroxysteroid dehydrogenase type 3 deficiency: An enzyme needed to produce testosterone is impaired, but the body may still produce significant levels.
- Ovotesticular DSD: A person has both ovarian and testicular tissue.
These conditions share a common thread: the athlete typically has XY chromosomes, internal testes that produce testosterone at levels well above the typical female range, and a body that can at least partially use that testosterone. Complete androgen insensitivity syndrome (CAIS), where the body produces high testosterone but cells cannot respond to it at all, is explicitly excluded from the regulations. An athlete with CAIS gets no performance benefit from elevated testosterone, so she is not considered a “relevant athlete” under the rules.
Common conditions like polycystic ovary syndrome and congenital adrenal hyperplasia are also excluded, even when they raise testosterone slightly above the typical female range.
Why Testosterone Is Central to the Debate
Testosterone drives many of the physical traits that separate male and female athletic performance: muscle mass, bone density, oxygen-carrying capacity, and strength. In typical women, blood testosterone levels sit well below 2 nmol/L. In typical men, levels range from roughly 7 to 30 nmol/L. Some DSD athletes naturally produce testosterone in the male range while competing in women’s events.
The core question is whether that elevated testosterone provides a meaningful competitive advantage. For conditions like PAIS, where the body partially responds to testosterone, the answer is complicated. The athlete’s cells use some of the hormone but not as efficiently as a typical male body would. For CAIS, the testosterone is essentially inert. This biological nuance is what makes blanket rules so contentious. A single testosterone number doesn’t capture how much of that hormone an individual’s body actually puts to use.
How the Rules Have Changed Over Time
World Athletics first tried to regulate hyperandrogenic female athletes in 2011, setting a testosterone ceiling of 10 nmol/L. Indian sprinter Dutee Chand challenged the rule at the Court of Arbitration for Sport (CAS) in 2014, and the court suspended it, finding insufficient evidence that elevated testosterone alone conferred a clear advantage.
World Athletics responded with a narrower regulation in 2018, targeting only athletes with specific 46,XY DSDs and testosterone above 5 nmol/L. South African middle-distance runner Caster Semenya appealed this version. CAS upheld the regulation in 2019 but acknowledged the science was not conclusive and encouraged further research before full implementation.
The rules tightened again in March 2023. The current testosterone limit is 2.5 nmol/L, measured from a blood sample drawn between 8 and 10 a.m. after two hours of rest. Athletes must maintain levels below that threshold continuously for at least 24 months before they can compete, a significant jump from the six-month window required under the 2019 version. The regulations now also apply to all track and field events, not just a restricted set of distances.
What Compliance Looks Like for Athletes
To meet the testosterone threshold, DSD athletes typically use one of several medical approaches. The most common and accessible option is a standard combined oral contraceptive pill, which suppresses the body’s own hormone production. Other options include injectable medications that shut down the hormonal signals from the brain to the gonads, lowering testosterone over a period of weeks. Some athletes have undergone surgical removal of internal testes, which permanently eliminates the testosterone source but is irreversible.
Each option carries trade-offs. Hormonal suppression can affect mood, energy, body composition, and bone health. Critics of the regulations argue that requiring healthy athletes to take medication or undergo surgery to compete is ethically problematic, especially when the performance advantage from their specific condition may be modest or uncertain. Supporters counter that some form of categorization is necessary to preserve meaningful competition in women’s sport.
Why the Issue Remains Unresolved
The science, ethics, and policy around DSD athletes resist easy answers. A person with a DSD did not choose their biology any more than an unusually tall basketball player chose their height. Yet sports have always drawn lines to create competitive categories, and sex-based categories are among the most fundamental.
The CAS panel that upheld the 2019 regulations described the rules as discriminatory but “necessary, reasonable and proportionate” to protect fair competition in the female category. That tension captures the state of the debate: nearly everyone involved agrees that DSD athletes are women, that the rules impose real burdens, and that the underlying science is still evolving. What they disagree on is where fairness lies, and for whom.
Athlete surveys show divided opinions even among elite competitors. Some feel strongly that testosterone-based rules protect the integrity of women’s events. Others view them as invasive and arbitrarily punishing athletes for natural biological variation. The regulations will almost certainly continue to shift as new research emerges and as individual athletes challenge the rules through legal channels.