Contrary to popular belief, breastfeeding does not make breasts sag, according to research carried out on US women seeking plastic surgery.
Pregnancy may make breasts sag, but nursing does not make it worse
However, one of the principal contributors to breast sagginess is getting pregnant in the first place.
Smoking and age also play a role, the American Society of Plastic Surgeons Conference heard.
Women can now breastfeed without fear for the future of their breasts, author and plastic surgeon Brian Rinker said.
Dr Rinker said he decided to carry out the study after many of his patients demanded he "fix what breastfeeding did to my breasts".
With colleagues from the University of Kentucky, he studied 132 women who had sought breast lifts or augmentation between 1998 and 2006.
The majority of them had been pregnant at least once. Nearly 60% had breastfed at least once.
The research team evaluated the patients' medical history, height and weight, pre-pregnancy bra cup size and whether they smoked.
There was no difference in the extent of ptosis - the clinical term for breast sagginess - between those women who had breastfed and those who had not.
But other factors did play a role. The degree of sagginess increased for each child carried by the woman. Smoking was also identified as a contributor.
"Smoking breaks down a protein in the skin called elastin, which gives youthful skin its elastic appearance and supports the breast," Dr Rinker said.
"So it would make sense that it would have an adverse affect on the breasts."
Other research has found that failure to wear proper sports bras may also play a part in breast sagginess.
Mr Kevin Hancock, a consultant plastic surgeon based in Liverpool, agreed with the analysis.
He said pregnancy often initiated changes to breast size, which could stretch the tissue and make sagging more likely.
This often became an issue when the breasts began to shrink when they stopped producing milk - a process known as post-lactation atrophy.
However, he said: "There is no evidence that breastfeeding makes any difference to these changes."