Since breasts are largely made up of fatty tissue, the only way to tighten up the fat is to lose weight overall through a healthy diet and regular aerobic exercise. In the meantime, you can perform strengthening exercises that will build up the underlying chest muscles and improve the look of your breasts.
Swim to get a good cardiovascular workout and work your arm and chest muscles. Swimming can help you burn fat and build muscle in your upper body. Aim to spend two and a half hours per week swimming to lose fat around your breasts.
Sit in an easy cross-legged position on the floor and bring your palms together in front of your chest for a chest-strengthening Kundalini yoga move. Inhale, and then while you are exhaling, press your palms together as hard as you can until your arms are shaking. Inhale and repeat 10 times. Vary the move by bringing your forearms together in front of your chest and as you exhale, press your forearms together. Repeat 10 times. Keep your shoulders down for both variations.
Stand facing a wall, arm's-length away for a wall press. Place your hands on the wall about shoulder-width apart and at shoulder height, fingers pointing toward each other. As you exhale, lean into the wall keeping your back straight and your heels on the floor. Inhale, and with slow control, straighten your arms and push yourself back to the start. Complete 10 repetitions.
Practice pushups to tighten the muscles around your breasts. Start with pushups on your knees until you are able to perform a full push-up. Perform five pushups in each set, resting between sets and aiming for four sets in total. Work to eventually reach three sets of eight to 10 pushups.
Lie on an exercise bench or stability ball, holding a 5- to 7-pound dumbbell in each hand. Bend your elbows and position the dumbbells on either side of your chest. Press the dumbbells up while straightening your arms. Lower the weights back to your chest and repeat until fatigued. Work your way up to three sets of eight to 10 reps.