Their own weight causes them become saggy. Breasts aren't composed of much muscle at all, they're pretty much fat. Sunlight as well causes them to be saggy, as with all of your skin. Exposure to the UV rays of the sun causes any skin to become wrinkly. After say, 60 something years of being alive, you'll see the difference in comparison to when you where 18.
if you dnt wear a bra more often it can make them saggy but dnt start sleeping wit a bra either cuz tht can be bad. jus wear one during the day wen u r out and about but jus not to bed
Not wearing a bra more often can cause them or meaby the bra is not soporting them like it should?
The most common reason that I've heard of is weight loss.