"Pulling"

Mothers encourage young girls to do it, and in the UK may pay other older women do it to them at first, teaching and encouraging them to do it themselves, until they can do it on their own. They are taught to pull daily for a period of weeks. The process can cause an enlargement of as much as 12.5 cm (5"). The expansion (like DIY foreskin restoration) is not "stretching" but the stimulation of cell growth through tension.

Some young girls, when they are unsuccessful using their fingers alone, resort to the use of strings, which can cause damage.  Some women also feed girls a special food in powder form to aid the process. The nature of the food is not known.

Harmful effects include:

pain ulceration loss of tissue (through the use of string, presumably by cutting off the circulation, causing necrosis - cell death). when imposed on a non-consenting girl, violation of human rights

There are no figures for how common labial pulling is. The enlarged labia of women of the Khoikhoi people of the Kalahari desert (the term "Hottentot" is now frowned on) are a genetic trait (medical name: sinus pudoris or macronympha).