A toddler grew breasts and began experiencing signs of early puberty after she was accidentally exposed to her transgender father’s hormone therapy.

The unnamed child, 3, was brought to doctors in Denmark after showing signs of extremely early puberty that had persisted for six months, including enlarged breasts and nipples and premature vaginal discharge. 

Her father told physicians the pair had frequent skin-to-skin contact, a key part of bonding. 

The parent, however, was also undergoing estrogen therapy as part of a gender transition from man to woman. The father used estrogen cream across their body, including chest, abdomen, shoulders and thighs daily.

Doctors warned that the girl had been absorbing the estrogen, a female sex hormone, from skin contact, triggering premature puberty.

This set off a cascade of potentially dangerous side effects.

Premature puberty in females, before the ages of eight years, can lead to a higher risk of certain cancers, including breast and endometrial cancers, mental health problems, behavioral issues, eating disorders and substance abuse. 

A young girl grew breasts and experienced vaginal discharge after exposure to her father’s gender-affirming hormone drugs (stock image)

The father had used a spray containing 6.12mg of estradiol, the most potent form of estrogen, on both forearms daily. 

But seven months before the child was taken to the doctor, the father had switched to using a 3.75mg estradiol gel. 

Along with enlarged breasts and nipples as a result of the exposure, an ultrasound revealed her uterus and endometrium, or lining of the uterus, had increased to a size seen in older females.

Her bone age was estimated to be 7 years old, while she was 3ft 6in tall and weighed 43lbs, the doctors reported.

The average three-year-old in the US is between 2ft 10in and 3ft 4in tall and weighs around 26 to 38lbs.

To treat the case, doctors asked the father to switch from rubbing in a gel to using a patch on the skin to receive estrogen.

They reported that after the change was made, the girl experienced a regression of breast development and a normalization of growth speed and pelvic size. 

The father had been applying an estrogen gel daily to his chest, abdomen, shoulders and thighs (stock image)

In the study, the researchers from Aalborg University Hospital said: ‘Transgender persons should be thoroughly informed of the risk of transmission of transdermal hormones and be advised to wash hands, use gloves and avoid skin contact shortly after hormone application. 

‘Patients with children must be warned of the risk and Gender Clinics should consider the possibility of prescribing alternative routes of administration such as tablets or patches in high-risk patients.’

About 1.5million Americans identify as transgender, although it is not clear how many of these are parents or use estrogen gel.

Women may also use estrogen gel to combat symptoms of the menopause, although this tends to be at lower doses.

In a similar case revealed in Sweden last month, a 10-month-old baby girl grew a ‘micropenis’ after she was exposed to her father’s testosterone.

Her father had been using testosterone to boost levels of the hormone and rubbing it into his body using a gel.

He was also practicing skin-to-skin contact with his baby, leading to testosterone being passed to the infant.

Revealing the case from 2023 in a report in a journal, the team warned parents should be ‘thoroughly informed’ of the risks of transferring hormones to their children.

They advised washing hands after the application of hormones, wearing gloves, and avoiding close contact immediately after use.

In high-risk cases, they added, clinics providing care for transgender patients should consider alternative treatments, such as tablets or patches.