Teenage girls are being directed to a new online reference tool that helps them check if their vulva looks normal.
Available on the sexual health charity Brook website, the resource gives visual examples and advice on how female genitals change in puberty.
The health experts who designed it say they hope it will give body confidence and discourage girls from wanting "designer vagina" cosmetic surgery.
These operations should not be performed on girls under the age of 18.
Most cosmetic vulval surgery – labiaplasty to reshape or shorten the vaginal lips or labia – is performed by private medical practitioners and can cost thousands of pounds.
Occasionally, an operation may be carried out on the NHS if the vaginal lips are abnormal or are causing the woman distress or harming her health.
GPs are not meant to refer girls for surgery for cosmetic reasons alone.
According to NHS figures, in 2015-16, more than 200 girls under 18 had labiaplasty and more than 150 of the girls were under 15.
Ms Louise Williams, clinical nurse specialist at University College Hospital and co-lead of the project, said: "This educational resource will help young people to understand their vulva and how it develops during puberty, particularly if they are worried about how they look or feel.
"We hope it will reassure young people that vulvas come in a variety of shapes and sizes, and if they need advice and support, they can know where to go."
Dr Naomi Crouch, from the Royal College of Obstetricians and Gynaecologists and the British Society for Paediatric and Adolescent Gynaecology which was also involved in the project, said: "There is absolutely no scientific evidence to support the practice of labiaplasty and the risk of harm is significant, particularly for teenagers who are still in stages of development both physically and psychologically.
"We hope this resource will provide information for girls and young women that their vulva is unique and will change throughout their life, and that this is entirely normal and healthy."
Designer vagina – what can go wrong
A labiaplasty can occasionally result in:
- scarring of tissue
- reduced sensitivity of the genitals
Any type of operation also carries a small risk of:
- developing a blood clot in a vein
- a bad reaction to the anaesthetic