[/b]Most women experience a sagging or dropping breast at some points in their lives. This is a natural and inevitable process. Some call it sagging, some drooping and some empty or flat chest.
Women are often bothered when they breasts begin to sag as they feel it makes them unattractive.
A lot of things can contribute to premature sagging of the breast and some have to do with your behavior. So, if you avoid these behaviours, your breasts will be better off.

1[b]. Smoking:[/i]
Even your breasts can’t escape the damage cigarettes do. Smoking breaks down elastin, the protein fibers in skin that lend it firmness and elasticity. Smoking also damages breast skin the same way it does the face, depriving it of oxygen and nutrients.
2. Wearing the wrong bra size:[i]

A good-fitting bra keeps your breasts in shape and enhances their appearance. If you’re going to wear a bra, it’s important to make sure it fits correctly because wearing an ill-fitting bra might cause extra sagging. Some women are wearing the wrong size bra. Stop in a lingerie shop and ask for a fitting just to make sure you’re wearing the right bra for your shape so you can make sure your bras aren’t doing you more harm than good. It’s also important to remember to replace old bras before they lose their support, too.
3. Weight Fluctuation:[/i]
Weight fluctuation is a big factor when it comes to sagging boobs. Each time you gain and lose weight, breast tissue slacks more. An unhealthy diet can cause stretching of the breast tissue. Weight gain from an unhealthy diet rather than weight gain from muscle-building exercise can result in stretching of the breast tissue.
4[b]. High-Impact Workouts:[/b][i]
Running, biking, playing sports and doing any other exercise causes your breasts to bounce. If you do it often enough without wearing a good sports bra, they may sag prematurely. A sports bra should contain your breasts securely against your chest so that bouncing is kept to a minimum.
5. Skipping Sunscreen:[b][/b]
Sunburn is never fun, UV rays hitting the sensitive underside of your breasts encourages serious drooping later on in life. Exposing your breasts to UV rays without a protective coating of sunscreen can stretch out the collagen and damage the skin.

feel free to add other reasonable causes