It is often assumed that breast feeding causes droopiness of the breast, or breast ptosis. However the evidence is that it is not a major factor. Although, it is true that the risk of ptosis increases with each pregnancy.
However other factors are more important. For example age, being overweight, increased number of pregnancies, smoking , and larger pre-pregnancy breast size, are all much more important than breastfeeding in creating postpartum breast droopiness.
This is good news for mothers who want to breast-feed because it is not likely to increase ptosis.