We hate to deliver depressing news, but the fact is, some B.reast sag is inevitable. Having a baby, B.reastfeeding, and racking up more birthdays all contribute to a loss of elasticity of collagen, the connective tissue under the skin—leaving your set more deflated than firm. Sag can also be a matter of genetics. If your mother had a droopy pair, you might be predisposed to one, too (thanks, Mom!).

Here’s the thing: Some boob behaviors that seem like they have nothing to do with sag can actually contribute to it—so if you avoid them, your B.reasts will be better off. And considering that a recent UCLA study found that B.reast tissue ages two to three years faster than the rest of your body, you might want to quit any habit linked to a flaccid pair—like these.

1. Crash Dieting

Cycling back and forth between the same five to 10 pounds probably won’t make a dent in your set. But yo-yo dieting 30 or so lbs over and over? Definitely. Each time you gain and lose weight, B.reast tissue becomes more slack, kind of like old tights, says Michael Edwards, M.D., a B.reast surgeon and president of the American Society for Aesthetic Plastic Surgery.

2. Smoking

Even your B.reasts can’t escape the damage cigarettes do. “Any amount of smoking weakens and ages skin by decreasing the blood supply to the skin surface,” says Edwards.

3. Skipping Sunscreen

Exposing your face to UV rays without a protective coating of sunscreen can lead to premature wrinkles, and it has the same effect on B.reast sag by stretching out collagen and damaging skin, says Edwards.

4. Wearing an Unsupportive B.ra

Whether it’s the boulder holder you wear during the day or the sports B.ra you change into at the gym, not sporting proper support is a big reason for droop. “The more your B00bs bounce around, the more stressed B.reast skin and collagen become,” says Edwards. Stop in a lingerie shop and ask for a fitting just to make sure you’re wearing the right B.ra for your shape.

5. High-Impact Workouts

The research is scant right now, but some experts say that the back-and-forth repetitive motions that happen when you run or do a similar workout can lead to a breakdown of B.reast collagen. But before you swear off the track or treadmill,read up on the details (and keep in mind that exercise helps you keep up a youthful appearance in other ways).