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Sex characteristics are any of the traits associated with biological sex. They are many and can refer to the chromosomal, gonadal, hormonal, and anatomical features of a person, which include primary characteristics such as reproductive organs and genitalia, and secondary characteristics such as muscle mass, hair distribution, breasts, …

• ‍Primary sex characteristics: Primary sex characteristics or sex organs are organs directly involved in reproduction which are present at birth. These include external and internal genitalia such as the penis and testes in males and the uterus, vagina, and ovaries in females.

• ‍Secondary sex characteristics: Secondary sex characteristics are features that are not directly concerned with reproduction and which develop later in life, such as voice quality, the development and repartition of body hair, the development of breasts, acne, and body odour.

The development of both is controlled by sex hormones produced by the body. Hormones that express sex differentiation in humans include estrogens, progesterone and androgens such as testosterone.