Clinicians may prescribe testosterone for females desiring to look more like men, or oestrogen for males seeking to look more like women. The aim is to raise the level of these hormones to around that naturally seen in the opposite sex.

A female person who takes testosterone will experience:

• lowered fertility
• growth of facial and body hair
• voice deepening, as the vocal cords thicken
• clitoral enlargement
• irregular or no periods
• bigger muscles and greater strength
• redistributed body fat, and less body fat overall
• an increase in the number of red blood cells.

Testosterone may also lead to:

• hair loss
• acne
• aggressive behaviour
• higher blood pressure
• cardiovascular disease.

A male person who takes female-typical quantities of oestrogen will experience:

• weight gain and increased body fat
• growth of breast tissue
• decreased sex drive
• lowered fertility
• enlarged prostate gland
• mood changes (depression, anxiety, irritability, tiredness).

Oestrogen may also lead to:

• impotence (inability to get an erection)
• a higher risk of blood clots and stroke
• swollen hands and feet
• type 2 diabetes.

Differences in male and female DNA mean that sex hormones do not have the same effect on people of the opposite sex. That is, testosterone taken by a female person will not have exactly the same effects as either the natural testosterone produced by a male person, or extra testosterone prescribed for a male person with unusually low natural levels. And similarly for oestrogen taken by a male person.

The long-term impacts of taking cross-sex hormones for many years, especially when started as an adolescent, are largely unknown.

If someone decides to “detransition” (re-identify as their biological sex after medical transition), many of the changes they have experienced will be irreversible. Males who have taken oestrogen will continue to have breast growth. Females who have taken testosterone will continue to have facial hair, clitoral enlargement, and a deepened voice. In both sexes, fertility may be permanently impaired.  

Those for females include:

• oophorectomy (removal of the ovaries)
• double mastectomy (the removal of both breasts, with or without nipple removal)
• vaginectomy (removal of the vagina)
• hysterectomy (removal of the womb)
• cosmetic facial surgery (options include implants to make the brow, nose or jaw more prominent).

Those for males include:

• orchiectomy (“castration”, removal of the testicles)
• penectomy (removal of the penis)
• tracheal shaving (surgery to make the Adam’s apple less prominent)
• cosmetic facial surgery (options including shaving bones to make the brow, nose and jaw less prominent).

There are also a number of cosmetic procedures that seek to mimic the genitals of the opposite sex. These may achieve a satisfactory aesthetic result, but medical science is not able to construct functioning sex organs.

The two main operations for men who seek the genital appearance of a woman are “vaginoplasty” and “vulvoplasty”.

The most common type of vaginoplasty is a surgery in which the testicles and internal parts of the penis are removed. The scrotum, penile skin and nerves are used to create a simulacrum of a vagina and labia in a newly made cavity in front of the rectum.

If the man took “puberty blockers” when younger in order to avoid the usual changes of puberty, such as his voice breaking and beard growing, his genitals will still be child-sized. There will probably not be enough skin to create a neovagina. In this case, part of the stomach or bowel lining may be used to give greater depth.

In a vulvoplasty, only the external female genitalia are mimicked, without creating a neovaginal cavity.

Surgery to give women the appearance of men is harder, and done less often. The two main options are:

• metoidioplasty: this operation takes advantage of clitoral growth caused by taking testosterone. Internal ligaments are cut to allow the clitoris to stick out more, so that it looks like a small penis (the woman will still urinate from the original opening, called the urethra, not from the end of the enlarged clitoris).
• neophalloplasty: this requires a series of operations, with a very high rate of complications. The first step is to cut flesh from another part of the body, usually the forearm, thigh or abdomen, and craft it into a cylinder. This is attached to the genital region, perhaps with a neoscrotum containing prostheses that look like testicles. If the neophallus is to be used for urination, the woman’s urethra will have to be extended into it, which takes more operations. Enabling it to become erect requires a mechanically controlled implant.

People who have had any of these surgeries are likely to need ongoing care. This must be provided by specialists in transgender surgery, rather than specialists in the care of either male or female sex organs.

For example, the vagina is a self-cleaning and self-lubricating organ with a muscular lining that is capable of stretching enough to allow a baby to pass through it at birth. The medical specialists in care of this organ are called gynaecologists. They will not know anything about the care of a surgically constructed neovagina, which will require regular dilation and careful cleaning. The doctors best placed to advise on any problems are probably the surgeons who specialise in performing those genital operations.